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338 LM Improved gain twist barrel

Jeffvn

Gunny Sergeant
Full Member
Minuteman
Apr 26, 2004
1,185
28
65
Las Vegas, NV
I have been posting about my new rifle in a different forum, but thought you guys might like to see it also.

My 338 Lapua Magnum Improved rifle was designed from the ground up to shoot some of Noel Carlson's ultra high BC lathe-turned, banded solid bullets out to and hopefully beyond 2,000 yards at my home desert range in Nevada, elevation 2,100 ft. The rifle has a 32" (not including break) Bartlein gain twist barrel (starts at a 12" twist at throat and exits the muzzle at roughly a 5.4").

Here is a picture of a dummy round using blown out brass from the same reamer and one of the 338 7 caliber long ZA bullets seated to roughly proper length. The tip of the ZA has been flattened by my gunsmith to prevent injury . . . as when I shook it out of the box it hit my palm point first and drew blood . . . nasty and TRUE.

Here she is on the left, next to the 7WSM and 284 Winchester (with 180 Berger's seated to their shooting length in my 7WSM and in my brother's .284 Winchester. On the left is a piece of new 338LM brass and a hydraulically blown-out case to my improved reamer design.

The 338 total length is right at 4.135 inches

IMG_1153cropedmed.jpg


This is what the rifle looks like. Manners T2-A in Coyote Brown, Barnard PL 338 single-shot action, 32" Bartlein gain-twist barrel, March 6-60X scope w/ tactical ranging reticle, and a removable Badger FTE break....(for the AAC Titan Suppressor that is on order for it). The rounds shown with the rifle below are the 338 LM Improved with 7 Caliber ZA, my 7WSM with Berger 180, and a .308 with 170 Lapua Lockbase.

IMG_1164crop2med.jpg


Range Day-1 I ran the first 8 rounds through the rifle. The bullets were GS Custom 295 grain SP lathe turned solids. I was just trying to get a feel for the rifle and see if I could find the pressure limits with H. Retumbo powder (suggested to me by Greg Tannel). The Temp was a bit spicy, 92 degrees in the shade when I started and 96 when I stopped (as in from 7:45 am to 8:45 am).

I loaded up 2 rounds with 95 grains, 2X 96, 1X 97, 1X 98, 1X 99, and 1X 100 grains of H. Retumbo. To my surprise, I never found a cratered primer or ejector mark on the brass; no pressure signs at all. So 100 grains is well within the pressure limits of this particular firearm; the 100 Grains was producing 2,980 fps. I wanted to push it a touch faster to see if 102 was near the pressure limit and what it mean in terms of velocity. My original goal was to get close to 2,950 fps for my accuracy load with the 300 grain bullets.

Amazingly, the last 4 shots, 1X each at 97, 98, 99, and 100 grains, formed a nice little .75" outside edge to outside edge roughly 1/2 MOA clover-leaf group on the target. The slowest load (95 grains) produced a velocity of 2,840 fps; the highest (100 Grains) produced 2,980 fps.

How confident am I in those velocity numbers - VERY. I recently picked up a second CED Millennium chronograph, and had them set up end-to-end so both could measure the same shot. They were producing different numbers for each shot (to be expected), but the velocity differential was consistent shot to shot. The numbers shown above are the average of the two chrono results.

Range Day -2. This day was even hotter than Day 1. Temps ran from 96 to 102 in t he shade, so velocities were also higher. Again, no pressure signs at all. The loads with these bullets are running with low pressure and pretty uniform velocity (pretty tight ES and SD). I have gotten a uniform (only 3 shot groups so far) roughly 1/2 MOA groups at 100 yards, for ALL loads between 98.5 grains of Retumbo to 100 grains of Retumbo (1/2 grain increments). Every one of the 1/2 grain groups measured outside edge to outside edge .75" or slightly less.

Sadly my load development has stopped for the short term until I can get more of the GS Custom 295 SP bullets. I only purchased 50 and that has not been enough to provide me with definitive load development results. I am satisfied that my 1/2 MOA results are solid, but there might be a better load out there and if so it would be nice to find it. At very long ranges I would prefer 1/4 MOA to 1/2 MOA any time. Granted, the shooter makes up for a ton more accuracy at the target then that, but it's a confidence thing to me. (I am holding by my last 18 bullets to shoot steel out to 1,800 yard with my brother and a friend from Houston.)

I will post more from my Desert shooting trip and loading results with the rifle as they are known.
 
Re: 338 LM Improved gain twist barrel

<span style="font-size: 11pt"><span style="font-family: 'Comic Sans MS'">Is this rifle built specifically to shoot the GS Custom bullet, because I would not think that ANY conventional bullet could with stand the rpm generated by a 5.4" rate of twist (393,333 rpm) at 2950 fps.
Does the GS solid require this much rpm</span> to stabilize?

Dave</span>
 
Re: 338 LM Improved gain twist barrel

no it doesnt, but he built this rifle to shoot the ZA 7 cal bullets, not the GS customs...

A gain twist barrel like this will tear apart any jacketed bullets also, so only solids can be shot with a barrel like this. This means your bullet choices are very limited. As far as i can tell, the ZA bullets are not ready for commercial sale yet either, meaning the GScustoms (with 6 month wait) are about the best of VERY FEW options im aware of atm...

 
Re: 338 LM Improved gain twist barrel

Grouper,

The commercial version of both the ZA 6.5, and 7.0, in 375, and 338 caliber will be available for public purchase within two weeks. A 30 day delivery turnaround time is anticipated for order processing. I am finalizing alloy selection as we speak, and the outcome of these tests will also determine the ZA-PDT hunt bullet material shell choice.

The limiting factor on the ULR projectile, until recently, has been barrel availability. There will be some information posted in a few days regarding the ZA-VGT barrel that will finally address this.

Jeff,

"The tip of the ZA has been flattened by my gunsmith to prevent injury . . . as when I shook it out of the box it hit my palm point first and drew blood . . . nasty and TRUE."

... Once again, sorry for the blood-letting. ZAs now have a .010" radius on all tips. Keep an eye on the mail, and enjoy your coming shoot.

Best,
Noel
 
Re: 338 LM Improved gain twist barrel

I shot up to 104 grains of Retumbo under 300 grain Bergers in my 338 Lapua Improved and that just showed an ejector mark, but the primer was fine. Velocity was almost 3100 fps.
 
Re: 338 LM Improved gain twist barrel

Jeff,
Sorry about the wait. Really did want to get you those bullets before your brother arrived. We are so busy that we are 2 months behind. Sorry guys, but just cannot keep up, and we are not willing to speed things up and sacrifice quality. Once the shop here is up and running we will be able to get orders out in a few days, but that is still a little ways off.
One recommendation I have is to work your load up to speed first, then seat the bullet all the way out and touching the lands to start tuning the load for accuracy. Work your way back off the lands until you get the groups you like. Hope that helps.

groper,
Thanks for answering that question. The 295 will work in anything faster then an 8 twist, and no gain twist is needed. Just for those who would like to read up, here is the technical data page: http://www.gsgroup.co.za/338295SP142.html
 
Re: 338 LM Improved gain twist barrel

This gain twist barrel was not designed for the GS Custom solids, but the 295 SPs are not suffering any visislbe advers efffectsw from the 5.4" exit twist so far.

Extremist458...the supply chain is what it is, I do not have to like it, just live with it, just like you - hense the large second order.

I will post more details and a picture or two tomorrow after I send some of the GS Custom 295 SPs downrange at 1,350, 1,550, and 1,760 yards. My shooting group (this trip it is me, my brother (Jsvanniel on the Hide), TopoSniper from here on the Hide and one of my F-Class shotting frineds (John L.) visited the site today to verify the road's passability and each of the chosen target locations. We are gtg for tomorrow.
 
Re: 338 LM Improved gain twist barrel

ran into some issues on teh rifle side, not sure exactly what is happening, so i didn't shoot to 1,760 with the 338 LM Improved.


I get to 1 mile with my 7WSM, and my brother got there with his .284 Winchester, so I thought I would show off that picture.

1miletarget.jpg


ONe mile target. Light hits are from .284; darker hits from 7 WSM (14 hits total).

JonJeffRandy6262010-1.jpg


Standing on the firing point; mile target is past the intermediate hill and just above right shoulder of person on far right.

2010-06-26100741.jpg


from the target, looking back to the firing point, past the intermediate hill, the firing point is between my thumb and index finger.
 
Re: 338 LM Improved gain twist barrel

Description of issues with rifle?
 
Re: 338 LM Improved gain twist barrel

And that "person" on the right is TOPO-sniper! :) Woo F-ing Hoo that was a LOT of fun. 1800 yard new personal record.

ELR and afterward some Bookers and Padron Aniversario stogies....enjoyed it brother!
 
Re: 338 LM Improved gain twist barrel

I fired some of the 397 gr ZA 375 cals today from a 6.5 gain twist. The firing was done prone from the back of a P/U truck. Chiggers will eat yo ass up if you wallow in the grass. After getting a 100 yd zero I started popping rocks from 300 to 900yds. The velocity was running around 3070 and accuracy was sub-moa. I will stretch it further tomorrow. BC is lookin good, I was using 1.15 and was hitting everything I shot at out to 900.
 
Re: 338 LM Improved gain twist barrel

Hey Topo I was not going to "out" you unless you volunteered your identity. yeah that is pretty amazing. the flight time was in the 2.5 to 3 second range. MY pleasure to host you my friend. Any time we can get you out here you are welcome.

Fredo

The two observers that i had on the glass when I was shooting the 338 both noted that the trace looked very "odd" and then disappeared completely approximately 800 yards from teh firing point. They described it as a cork screw shape of trace. After talking with some other folks who have shot the GS Custom bullets, in this case the .375s, I'm inclined to think may be a bullet stability issue, but I have 11 rounds left and am going to see if I can verfiy that for sure.
 
Re: 338 LM Improved gain twist barrel

I fired the 6.5 cal ZA 397 gr. 375 projo out of the 13-6.5 gain twist barrel. I fired three rds at 2560 yds. Verticle despersion was around 1/2 moa. I did not try to dope the wind because it was switching around quite a bit. I recovered one rd and it had hit point first and looked like a drill bit. It was very obvios this thing was still spinning at very high RPMs.
 
Re: 338 LM Improved gain twist barrel

looks like ZA is winning the race atm
laugh.gif

look forward to hearing more augustus...
 
Re: 338 LM Improved gain twist barrel

Well I received a PM from Gerard regarding my possible bullet stability issues. Gerard does not believe the GS Custom .338 295 SPs will perform from the gain twist barrel on 338 LM Imporved, stating that the twist is far too fast, which is cause the bullets to not properly nose over. (That is my very rough paraphraseing of Gerard's email....so if I screwed up his statement blame me, not Gerard on his sdsicription of the problem).

So I will be testing the ZA fairly soon, and also the Predator 338s, to see how they react to teh gain twist barrel that I have on the 338 LM Improved.
 
Re: 338 LM Improved gain twist barrel

Sweet shooting. I have not made it to a mile yet. 1620 yards is my best so far. As I am always trying to learn more. I have a 7wsm as well. I take it your shooting your 7wsm out of a long action to be able to get those 180's seated out that for. In doing so what kind of powder, speed, pressures are you getting out of that?
 
Re: 338 LM Improved gain twist barrel

After talking with Noel he agreed that I can release some information of the current status of my testing of his 6.5 Caliber ZA Bullets. I thought it was a good time as any to bring this particular thread back from the dead (since the rifle and projectile pictured here is whatI tested again today).

Today I was testing 2 different versions of the ZA 6.5 caliber 338 projectiles (both are over 2" long One is 295 grains, and the other 276 grains) to see how they reacted in the denser air of the desert during winter.

A touch of background - I tested the 6.5 Cal 295 grain bullets this summer in 90 degree heat and velocities up to 3,150 fps. They shot well for me at all speeds out to my local range's longest testing distance with a solid back drop to see bullet impazct - 957 yards - and fully stabilized leaving crisp round holes in the target and plywood backer.

Today I shot the same bullets with the same loads in 30 degree temps and 25% humidity. Although they were stable at slower speeds, they DID NOT stabilize at roughly 3,000 fps or anything faster then that. It was not a total surprise, as we expected that might be the result in the denser air at colder temps. It sort of goes with living on the ragged edge of stability with the 5.4" twist that I have on the current barrel.

Interestingly enough, the ZA 276s, were fully stable at all speeds that I could produce today, right up to high pressure onset and a primer leaking (my signal to stop at 105% compressed load with Retumbo). I will shoot them again tomorrow to verify my velocity with the chronograph, but I am very confident that they were at 3,150+ if not a touch above 3,200 fps today. For those who are inquiring minds, I needed right at 15-6 MOA (MOA, not IPHY) to get from my verified 100 yard zero this morning to 957 yards.... I spotted a hole in the target at the bottom edge and am not sure when it showed up, so I want to be conservative in my BC estimates and holdover elevation.

hmmm you tell me the BC of that little beast if my velocity prediction is even close to accurate @ 3,200 fps. Here is a hint... start with a 0.9_ _..
laugh.gif


I'll shoot them again tomorrow, and report back with the velocities that I get on my chronograph. Fingers crossed, I might get some more at distance and some load development in tomorrow.

It looks like the ZA 6.5 caliber .338 solid is darn near ready for its public unveiling.... nice.

JeffVN
 
Re: 338 LM Improved gain twist barrel

SkyKing - Sorry I didn't mean to avoid your question on the 7WSM. I run mine out of a short action surgeon, but have them long-throated for the Berger 180s.

They are decidely NOT magazine length. I currently have two rifles in 7WSM, and have a .284 Winchester and .284 Winchester Improved sitting in my garage. In my F-Class rifle I run a year long load of 63.5 grains of H4831SC with GMM 215Ms; in my Surgeon short action I also have a long-throated barrel and one for magazine feeding. The long barrel uses a load of H1000, the grain weight is escaping my as I sit here typing but its something right at 67.7 H1000.
 
Re: 338 LM Improved gain twist barrel

Jeff, just as comparsion I know a guy who used LM-105 300gr 6.5cal solids in hes gain-twist TRG-42 several years ago. Package worked fine, and owner actually won our international sniper comp with it. MV:s he had were 2992fps, wasnt maximum load. BC was around .930 based on hes personal test shooting and actual drops.

Cant really remember all details- but it was built with Lothar stainless "John Holmes" progressve twist barrel. likely they have/had only one model in .338 caliber, I recall it was 7". Recommended twist in Möller´s page for LM-105 is 6.9".
Accuracy was ok, easily under 1MOA at 800yds, but sometimes there were occational sideways bullet impacts in a tight group!? with all other holes perfectly round. Air pressures were close to sea level.
 
Re: 338 LM Improved gain twist barrel

I shot 8 more of the 276s again today, to verify velocities so I can add more info to the mix from yesterday's range session. Today it was nearly identical as yesterday for weather. I shot my last 295 6.5 Caliber as teh 100 yard zero calibrator and get the ball rolling. I then shot 8 of teh 276s, watiing 2-3 minutes between shots.

The load was not a developed one, but simply one that I know was going to be safe (it was 2.0 grains less then what had popped/leaked on my yesterday). Anyway, the load produced an average velocity of 3,106 fps an ES of 30, and was a 1.0 minute load. Given that teh minute was mostly verticle,I suspect a real accurate load is nearby, but not the 103 grains of Retumbo thatI was using. I also think that today's velocities confirms my estimate yesterday of 3,150 to 3,200 fps for the top tested velocity.

FYI until I can do more at distance elevation and drop testing with known loads and color coded bullets, I'm calling the ball on BC on the ZA 6.5 at 3,200 fps as roughly .940. That does not suck too bad at all... But since that speed is not one thatI can or want to replicate it is likely of interst only to the 338/408 shooters where I believe 3,300 - 3,400 fps is easily within reach.

Noel wanted me to also mention that given my recent sucess success with the 6.5 caliber ZAs, he wants us the start testing the 7.0 caliber projectiles as soon as he can get some produced.

When I get them and shoot them, I'll let you know what they do.

JeffVN
 
Re: 338 LM Improved gain twist barrel

JL,

Within five degrees, do you know what the temperature was on the day of the competition you related?
 
Re: 338 LM Improved gain twist barrel

Noel, whats your take on loosing stability at high velocities? Reason i ask, is that this is contrary to typical projectiles static stability <span style="font-style: italic">increasing</span> the faster you drive them.

I have experienced no such phenomenon with my 6.76cal copper projectiles, yet both you and GSC have exhibited this behavior.

I have my own theory on why this is happening, i was hoping you might share yours?


 
Re: 338 LM Improved gain twist barrel

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Noel Carlson</div><div class="ubbcode-body">JL,
Within five degrees, do you know what the temperature was on the day of the competition you related? </div></div>
He did at least some test shootings before comp which was held in early July. Hard to know how bullets behaved during comp since reactive targets were used. Temps during tests must have been around 60-70F, air pressure very likely over 29,6. Finland is pretty flat country and average air pressure we have is 29,83.
But as I said, it was many years ago. I could ask if more detailed info is needed.

Jeff, about MV:s
At the moment, buddy gets 3120fps with VihtaVuori high energy N570 powder, 300gr Scenars and 32" long barrel- without having progressive twist. It should be about same burn rate than H870 has. So 3150 you expect to get sounds possible.
 
Re: 338 LM Improved gain twist barrel

JL

Thanks for your input and acknowledging the periodic stability issues suffered by the LM105s. I had heard similar information regarding them for years now.

At this point I feel compelled to be both blunt and completely honest on several issues. Here let me step up onto my soapbox and grab the Mr. Microphone.

I do not believe that a bullet that has intermitent stability issues is commmercially viable. Personally I do not want to buy a bullet that has known stability issues, if I could possibly avoid it or unless I go into the purchase knowing it is going to be an experiment.

I also have strong feelings about a manufacture selling bullets that it KNOWS are completely unstable, or are not stable when used above a certain velocity. Under those circumstances, I think the manufacturer should tell the consuming public that the projectiles are prototypes that may not be stable or specifically says what the velocity limit is and then the consumer can then decide whether they want to buy them.

I am NOT calling out any manufacturers in particular, if I was I would USE YOUR NAMES and directly call you out. I am merely saying what I believe as a consumer and what I think the rules ought to be. Also I want to make clear why I consider the ZA 295 NOT to be commercially viable in its current conditition; it does not work in all conditions and all rifles.

I like the fact that the folks who are currently riding the lightening and doing the prototype testing have the guts to post their results both good and bad. When you do that, you accept defeat as a step in teh right direction. Making progress MEANs you watch your best efforts fail and then going back to make changes and see if they work. Just like the ZA295 and 276.

Before I bought my gain twist barrel, I told Frank at Bartlein that I would not hold Bartlein responsible if the test was a complete failure. I KNEW going in that I might be buying the most expensive tomottao stake ever. Even so, you can't make technology gains without both expecting and observing failures in your designs.

All that having been said let me step down off my soapboax and say that because of the KNOWN stability issues with the ZA295, I do not consider the current design 6.5 caliber .338 295 grain a commercially viable projectile unless shot and used excelusively below say 2,900 fps. At that velocity, if you have a good twist on your rifle, say a 5.4 or 5.0 even better, then it works and it works dam well. But how many folks want to buy a rig designed just to shoot these solids and then run an artificial velocity limit of 2,900 fps. As such, I think this partuclar version of 6.5 caliber .338 ZA 295 is dead except for a good looking tiny paperweight on my loading bench.

Now the ZA276... that is a completly different scenario, at least to velocities of approximately 3,200 fps. This little bullet IS a beast inside that velocity range. If we can get them tested to 3,400+ fps sucessfully, then dam! Personally, I would LOVE to shoot them side by side against the LM105 in my rifle and see how they stack up.

JL

No doubt the newer powders are capable of pushing the bullets to much higher safe velocites than the older powders ever could. I have been trying to get my hands on the VV570 for af ew months with no luck so far. I'll keep trying as it seems to be able to do some great things on velocity yet not suffer from huge temperature swings.

Oh come on Grouper ... if you've got a theory on velocity-based stability issues, I'd like to hear it. How many rounds of your 6.7 caliber length bullets have been fired and at what velocities? What twist was used in the barrel?
 
Re: 338 LM Improved gain twist barrel

Groper,

I give you credit for sniffing out the baloney that has passed for innovation lately on some of the ELR threads. The eager members that have chastised you are going to look like Flat Earthers in good time. In the interim, why don't we keep our insights to ourselves until we can go beyond qualitative description, and into quantifiably documented, and scientifically interpreted/published fact? I believe that time is not far away.

I am content to leave them fumbling for a bit longer.
 
Re: 338 LM Improved gain twist barrel

Jeff you'll see a 2 to 2.5% increase in velocity using n570 compared to retumbo. I get 2.3% gain in my norma mag.
 
Re: 338 LM Improved gain twist barrel

VV N570 has 4000 Joules of energy per gram, similar burning rate but traditional non-nitroglycerine N100 series has 3700-3800J/g.
I dont know about other manufacturers, would be interesting to compare.

As an clarification for previous comment I wrote about LM-105 occasional instability -one sideways impact was sometimes found in a very decent size group as I said- but in rather long 800yds range. Apparently projectile lost its stability just before hitting TGT.
Just wanted to point this out since my comment was ambiguous.
 
Re: 338 LM Improved gain twist barrel

JL and CK thanks for the clarification.

That distance ... approximately 800 yards before instability... is consistent with what I saw with the ZA 295s, as it hit into the dirt at least 40 yards short of the 957 yard target, and then ricocheted into the impact berm next to the target. Same thing with the instability witnessed by my spotters on shooting the 295SP GS customs which lost stability and were not seen again sometime at or after approximately 800 yards or so when we were in the desert.

No doubt I truly would like to test some of that VV570...

JeffVN
 
Re: 338 LM Improved gain twist barrel

Jeff,

I think the 800 yard instability ranges are coincidence, although that chance occurance does provide a convenient baseline for comparative tolerance to elevated air density.
 
Re: 338 LM Improved gain twist barrel

In my .408 CT, N 570 give me 30 m/s more compared to N 170 with same pressure & accuracy.
 
Re: 338 LM Improved gain twist barrel

Well if you dont want to share your theories, thats ok i can understand that.

Mind if i share mine tho? ok no worries and keeping in mind im making alot of educated assumptions here...

With the twist rates you are using, there is no way its a static stability problem. This means its a dynamic stability problem, which is consistnt with failings down range, rather than at the muzzle.

Most likely problem, is a magnus induced dynamic issue. You have large moments due to longer than typical nose and boattail, and also an unusually large magnus force for the same reason but also compounded by the very high spin rates your using. Am i warm?

And jeff, i have stabilized a 6.76cal 385gr 375cal projectile from a 1:10 twist @ upto 3200fps. This was to prove a concept, i have no plans or expectations to create a commercial projectile this long for a 10twist barrel... the commercial versions are 6.4calibers from a 10 twist, and 7cal from an 8 twist
smile.gif










 
Re: 338 LM Improved gain twist barrel

Groper,

I am sure that you would agree... it is always a *balance* of "issues" ;-)

Congratulations on your results!
 
Re: 338 LM Improved gain twist barrel

Groper that is excellent; good for you. If you don't mind I have a few questions.

I'm just eager to see as many of these pills in the marketplace as possible. I suspect, but do not know for sure that limited comercial availableity of the high BC solids may play a part in the slow production schedules we currently have by Bartlein.

now for the questions...

Do you have an expected BC of the commercial version of your bullet yet? What about an expected / hoped for commercial release date for your 375? I can tell you from experience with the ZAs testing, that it seems to take at least 2X the hoped for tie to get them released.

Are you going to do a .338 version?

Is there any legal impediement to producing in your neck of the woods and selling in the USA? Or are you potentially going to try to produce in the USA or Canada?

I'm just eager to see as many of these high BC solids in the marketplace as possible.

JeffVN
 
Re: 338 LM Improved gain twist barrel

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeffvn</div><div class="ubbcode-body"> JL

Thanks for your input and acknowledging the periodic stability issues suffered by the LM105s. I had heard similar information regarding them for years now.

At this point I feel compelled to be both blunt and completely honest on several issues. Here let me step up onto my soapbox and grab the Mr. Microphone.

I do not believe that a bullet that has intermitent stability issues is commmercially viable. Personally I do not want to buy a bullet that has known stability issues, if I could possibly avoid it or unless I go into the purchase knowing it is going to be an experiment.

I also have strong feelings about a manufacture selling bullets that it KNOWS are completely unstable, or are not stable when used above a certain velocity. Under those circumstances, I think the manufacturer should tell the consuming public that the projectiles are prototypes that may not be stable or specifically says what the velocity limit is and then the consumer can then decide whether they want to buy them.

I am NOT calling out any manufacturers in particular, if I was I would USE YOUR NAMES and directly call you out. I am merely saying what I believe as a consumer and what I think the rules ought to be. Also I want to make clear why I consider the ZA 295 NOT to be commercially viable in its current conditition; it does not work in all conditions and all rifles.

I like the fact that the folks who are currently riding the lightening and doing the prototype testing have the guts to post their results both good and bad. When you do that, you accept defeat as a step in teh right direction. Making progress MEANs you watch your best efforts fail and then going back to make changes and see if they work. Just like the ZA295 and 276.

Before I bought my gain twist barrel, I told Frank at Bartlein that I would not hold Bartlein responsible if the test was a complete failure. I KNEW going in that I might be buying the most expensive tomottao stake ever. Even so, you can't make technology gains without both expecting and observing failures in your designs.

All that having been said let me step down off my soapboax and say that because of the KNOWN stability issues with the ZA295, I do not consider the current design 6.5 caliber .338 295 grain a commercially viable projectile unless shot and used excelusively below say 2,900 fps. At that velocity, if you have a good twist on your rifle, say a 5.4 or 5.0 even better, then it works and it works dam well. But how many folks want to buy a rig designed just to shoot these solids and then run an artificial velocity limit of 2,900 fps. As such, I think this partuclar version of 6.5 caliber .338 ZA 295 is dead except for a good looking tiny paperweight on my loading bench.

Now the ZA276... that is a completly different scenario, at least to velocities of approximately 3,200 fps. This little bullet IS a beast inside that velocity range. If we can get them tested to 3,400+ fps sucessfully, then dam! Personally, I would LOVE to shoot them side by side against the LM105 in my rifle and see how they stack up.

JL

No doubt the newer powders are capable of pushing the bullets to much higher safe velocites than the older powders ever could. I have been trying to get my hands on the VV570 for af ew months with no luck so far. I'll keep trying as it seems to be able to do some great things on velocity yet not suffer from huge temperature swings.

Oh come on Grouper ... if you've got a theory on velocity-based stability issues, I'd like to hear it. How many rounds of your 6.7 caliber length bullets have been fired and at what velocities? What twist was used in the barrel? </div></div>


Jeff,...Read the original Cheytac Projectile and barrel patent. It adresses the instabillity issues you have witnessed quite clearly.

LM and Noel Carson have been linked previously and he has also contacted me in regard to barrel manufacture. I concur with your observations and agree that the efforts of Grouper are perhaps as good an effort as we have yet seen. He has noted that a projectile for a conventional twist is a better idea like yourself rather than making something that has no mass appeal due to its exclusivity!

Have you tried talking with Dave Corbin? He is in the US and has vastly more experience with VLD/ULD design than just about anyone else?
 
Re: 338 LM Improved gain twist barrel

Emouse,

Now let's be clear about this; It was you who initiated contact with me by expressing interest in being the European distributor for ZA projectiles, with a particular interest in the 6.5 mm version.

The barrel discussion was more an issue of logistics to set up local manufacture. You volunteered yourself, and proceeded to contact Arthur Smith (who does not know you from Adam incidentally) to produce for you.

Regarding availibility of ZA barrels, watch for a separate thread to appear soon. The entire system will be released complete to any who are interested.
 
Re: 338 LM Improved gain twist barrel

Emouse

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> He has noted that a projectile for a conventional twist is a better idea like yourself rather than making something that has no mass appeal due to its exclusivity!</div></div>

I assume you mean Groper in this comment. I do not personally think it is a "better idea" to shoot standard twist solids as compared with the mega-BC version. If I gave that impression then I need to fix the post.

Although it will be nice to eventually shoot some good to very good BC solids from my standard twist 338LMs, and I plan to do just that when I get the time to buy some and load them up to see how they compare with my current stash of 300 gr SMKs and 300 grain Lapuas.

I'd personaly rather play the exclusivity game and shoot stunningly high BC bullets at target that are far away or shoot closer targets with stuningly flat elevations and limited wind holds.

I like shooting armor plate steel that sits over a mile away in the desert (I do it now with my 7WSM), and winning F-Class matches with the same rifle. With the ultra high BC projectiles, I can certainly fo the first, if we find a way to scale it down to 7mm or 6.5mm than I can do both desert shooting and F-Class with the smae rifle. I like no LOVE that idea.
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Like I said earlier, I think it will be excellent to see some of the standard twist projos fly and plan to use them in my own rifles when I get a chance to test some (Like preditor or Cutting Edge), but my real quest is that mega BC pill screaming through the desert to hammer steel 2,000 yard away from my 338LM Improved or eventually 3,000 yards away my 375 CheyTac.
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JeffVN
 
Re: 338 LM Improved gain twist barrel

Richard Corbin in no slouch either when it comes to that department. FWIW
 
Re: 338 LM Improved gain twist barrel

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeffvn</div><div class="ubbcode-body">Groper that is excellent; good for you. If you don't mind I have a few questions.

I'm just eager to see as many of these pills in the marketplace as possible. I suspect, but do not know for sure that limited comercial availableity of the high BC solids may play a part in the slow production schedules we currently have by Bartlein.

now for the questions...

Do you have an expected BC of the commercial version of your bullet yet? What about an expected / hoped for commercial release date for your 375? I can tell you from experience with the ZAs testing, that it seems to take at least 2X the hoped for tie to get them released.

Are you going to do a .338 version?

Is there any legal impediement to producing in your neck of the woods and selling in the USA? Or are you potentially going to try to produce in the USA or Canada?

I'm just eager to see as many of these high BC solids in the marketplace as possible.

JeffVN </div></div>

just quickly... the BC will be "mega", extremely similar to noels by the looks of things right now. calibers .338 thru 50cal. commercial release date, about 3 months. No problems with manufacture or exporting anywhere in the world UNLESS the destination country has import restrictions.

And now back to noels projectiles and barrel system... i have not been able to work out why you have chosen to persue this system using super fast twist rates Noel? Ill elaborate...

Some of Lutz Mollers bullets, and now some of your pre-production ZA bullets, have exhibited dynamic stability problems, and im guessing based on initial masses and dimentions, the designs are not too dissimilar from each other. Whilst Increasing the twist rate increases the static stability, it has little effect improving dynamic stability. Therefore chasing faster twists is not the answer, your just delaying its onset further downrange as the epicyclic arms still have inadequate damping and the precession will still increase in magnitude, it just takes longer to happen.

Its been scientifically proven, that the 3 largest factors influencing projectile dynamic stability are Magnus Moment, transverse radii of gyration and pitching moment. So how can increasing spin rate help improve any of these factors to improve dynamic stability? Theres a reason why it has not been done before (very long nosed and/or long boattailed projectiles), and its not because nobody could figure out how to build superfast twist gun tubes...

I can understand the gain twist, just not the high exit twist rate... care to elaborate why?







 
Re: 338 LM Improved gain twist barrel

Groper,

The reason that you have not been able to "work out" Jeff's reasoning, is that you have no foundation from which to draw conclusions. An appeal to "scientific" principles should prevent you from even trying.

We both know you have some distance to go in your concept development ;-)

Good luck to you in your work, and I will be happy to share information with you at the appropriate time.
 
Re: 338 LM Improved gain twist barrel

Groper

3 months; very nice. I look forward to seeing your bullets in April, 2011. Who are you going to use to distribute them?

JeffVN
 
Re: 338 LM Improved gain twist barrel

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: groper</div><div class="ubbcode-body">
Some of Lutz Mollers bullets, and now some of your pre-production ZA bullets, have exhibited dynamic stability problems, and im guessing based on initial masses and dimentions, the designs are not too dissimilar from each other. </div></div>

I`ve heard LRB J40 was showing similar symptoms back in the days- nice groups at 600yds or so.
But sometimes, with no obivious reason, occasional impacts 100yds front of target.
 
Re: 338 LM Improved gain twist barrel

Jeff or anyone else, have you shot the 276gr bullets from a slower twist barrel? a 7-8 twist barrel would most likely produce the same favourable results...
 
Re: 338 LM Improved gain twist barrel

Groper

No. I disagree that it would be sucessful, but do not want this thread to degerenate into a re-hash of earlier threads on twists rates. So I will just say that after you to do so, you can report back with your results.

I would not even know where to find the 7-8 inch twist barrel you suggest. No manufacturer in the USA that I have looked at, and I looked at a lot of them this morning, lists a 7 or 8 as available on their website. I tell you what, I am going to SHOT next week and will wander the halls and talk to the mfg reps for the barrel companies and see if they might do that. I will create a new thread and report back on my results in that new thread.

JeffVN
 
Re: 338 LM Improved gain twist barrel

Lilja lists a 338cal 7 twist on their website... http://www.riflebarrels.com/products/caliber_twist_rates.htm

not that id expect anyone to try it, i was simply wondering if anyone had actually tried a slower twist or 5.5 was the only thing that had been tried...

Reason i asked, is that its my personal belief that a 7 twist would be perfectly adequate at providing static stability for a typical VLD shape projectile of .338cal, 6.5calibers length weighing 276grains. This is NOT to say that the projectile would be 100% stable, as it may have dynamic stability problems not related to spin aswell.

Your results reflected something worth noting, where the 295gr didnt stabilize and the 276grain did. So clearly with regard to the lighter bullet, ill take another educated quess and say that moving the center of gravity forward reduced the pitching moment and therefore had a marked effect on improving the stability.

So in continuance, static stability can be approximated from the McGYro and Mcdrag twist calculators here;
http://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi
Its not appropriate for me to ask the dimensions of the bullet nor do i want to know, but you can measure it and see for yourself if your curious...

But not only this, I have also constructed many projectiles in this size, shape, mass and length using full 3D CAD models. One thing to realize when working with these models, is that there is not many combinations of nose length and taper, boattail length and taper, with an overall length of 6.5calibers, that will equal 276grains using 100% copper. The only real things you can play with are increasing boattail length whilst sacrificing nose length or vice versa to maintain that 276grains. The effect of playing with these geometry variables has a greater influence on dynamic stability than it does on static stability because of the different magnus moments and pitching moments generated by these different geometries. Ive seen that The axial and transverse moment inertias and the other varibles accociated with static stability, change very little with these changing geometries therefore leaving the static stability virtually unchanged with the exception of the pitching moment. This is why the miller fomula has such success with making its approximations based on length alone.

Using the CAD models, Ive been able to obtain the exact axial and transverse moments of inertia, transverse radii of gyration etc using 100% copper material. Then i used all this data in the <span style="font-weight: bold">full and unsimplified</span> gyroscopically spin stabilized projectile equations, rather than the miller formula or McGyro etc, and obtained very similar static stability factors (Sg),to what the McGyro formula predicts anyway. This was for a projectile described above, that averages around a 3.5caliber legnth nose, 2 caliber bearing length and that leaves a 1 caliber boattail.

Its not all smoke and mirrors... i can tell you the reason we do not see very long projectiles working, is because of dynamic stability problems, not static stability problems. The reason im saying this, is to prevent wasting time and money on even faster twist barrels. If 5.5 doesnt work, a 5 twist wont help, once you get out even further distances or higher velocities, where the dynamic problems will surface again...
 
Re: 338 LM Improved gain twist barrel

Im going to add a bit more to this in an attempt to help explain the problems with dynamic stability.

First the magnus;

Even though it might not be possible to accurately predict the Magnus force on a projectile, it is possible to visualize the mechanisms producing the Magnus force. The picture which is visualized is that of an aerodynamic body composing that of the actual projectile body surrounded by a warpable, viscous boundary layer. At all Mach numbers the Magnus force is generated to a large extent by the shape of the boundary layer, and the shape in turn is influenced greatly by the viscous twist or warpage due to the projectile spin. At zero angle of attack ( zero yaw) the warpage of the boundary layer due to its spin is axisymmetric about the main centerline, so that the resulting aerodynamic forces and moments are zero except for drag and rolling moment. At small angles of attack or yaw, the boundary layer thickens on the lee side of the projectile, but at zero spin the boundary layer maintains mirror symmetry. A normal force and pitching moment are generated, but the side forces and moments (magnus) remain zero. With spin, the thickened portion of the boundary layer twists in the direction of spin, all symmetry is destroyed, and a side force and moment are generated (magnus moment).

If a typical boattail is used instead of a straight cylinder or flat base tail, particularly at subsonic or transonic velocities, the boundary layer thickens due to the flow expansion over the boattail. (This flow expansion could be phycially observed in the CFD modelling shown by Bohem in his recent thread BTW.) The thicker boundary layer is distorted more by spin and thus a larger Magnus force is created. At supersonic speeds the Prandtl-Meyer expansion over the boattail holds the boundary layer to thinner values so that LARGE increases in Magnus force do not occur (but still increase). The large increase in Magnus force and moment caused by a typical boattail, esp at transonic velocities may be sufficient to destabilize an already marginally (gyroscopic) stable projectile by causing large changes in dynamic stability (from increases magnus and pitching moments) - Which happens to explain to a large extent, the tumbling we get with alot of projectiles going transonic, but not all of them!

Therefore, the longer the boattail and the more spin you have, the more magnus you generate and thus higher probability of dynamic stability issues. Which happens to explain to a large extent, why we dont see excessively long boattails in successful VLD projectiles.

Next the pitching moment and long noses etc... when i get some more time...
 
Re: 338 LM Improved gain twist barrel

Groper you certainly know what you are talking about when it comes to projectile design and flight and you are most probably right I have no clue about most of what you speak. Now please don't take this as me being rude because this is not my intent at all, but you have alot to say about other peoples designs both the ZA and GSC projectiles, which they are going out of their way to give us a sneak peak of while they are being developed and tested, but yet with all that you have to say I have seen no threads on any of your projectiles that you have said have been tested and are near completion, or have I just missed any thread you may have posted on your work?

Again please take no offence from my comments.
 
Re: 338 LM Improved gain twist barrel

Groper,

I think it is productive to explain the basic physics which act upon a spin-stabilized projectile. The exercise immunizes readers from some of the silliness that appears from time to time on these threads.

There is a recurrent pattern in your presentations that is a disservice however, and should stop. It takes the basic form of "I do not know, therefore I know.". Rather than pump, cajole, and prod my beta-testers (and others), publish what you actually know regarding the defects of your projectile as uncovered in testing... along with the remedies if it does not compromise propriatory information. On this you can speak with authority, and wiithout placing people in the uncomfortable position of refusing inquiries off-line on questions that you know can not be answered for any number of reasons.
 
Re: 338 LM Improved gain twist barrel

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeffvn</div><div class="ubbcode-body">Groper

No. I disagree that it would be sucessful, but do not want this thread to degerenate into a re-hash of earlier threads on twists rates. So I will just say that after you to do so, you can report back with your results.

I would not even know where to find the 7-8 inch twist barrel you suggest. No manufacturer in the USA that I have looked at, and I looked at a lot of them this morning, lists a 7 or 8 as available on their website. I tell you what, I am going to SHOT next week and will wander the halls and talk to the mfg reps for the barrel companies and see if they might do that. I will create a new thread and report back on my results in that new thread.

JeffVN </div></div>

Jeff, I'm not going to get into the middle of this whole thread etc....but to make a clarification on twist rates and manufacturers etc....besides the GT barrels, we have done 1-8 twist barrels in calibers like .338 etc....Nobody has asked for a 1-7 twist (we might have done it just cannot remember off the tip of my head).

Even though our website may only list a certain caliber and twist rate that doesn't mean we cannot do other twist rates. We are in the process of updating our website as well.

We have even made a .224 cal. barrel for Noel that had a 1-4.7 twist. You don't see it on our website but we can do things like this.

Our machines have the capability of doing twist down to and starting at 0 (zero) and thru out the whole twist spectrum. Also our machines have the capability of doing anything from a 2 thru a 24 groove barrel.

Any one that reads this keep this in mind. Tooling still plays a part. If you really insists on having a 15 groove 1-20 twist, 20mm cannon barrel that is 53" long we can do it but you will pay the $$$$$$ for it if we agree to do it. Some things cost wise and what customers are willing to pay are two different things. The customer and ourselves sometimes have to take a step back and say is this worth doing both cost wise and time wise.

When it comes to making tooling or doing prototype work once someone finds out the cost involved they back away from it. I didn't mean to go into a cost issue etc...but just wanted to clear up twist rates, calibers and what we can do or have the capability of doing and or have done. Just because it's not listed on our website doesn't mean we can or cannot do it.

Same as contours. We have some standard contours listed but have done just a slew of contours not listed. You just have to make a call and ask.

Jeff, Will also be at the Shot Show. Won't have a booth but will be walking around. If not walking around will be hanging out at the GA Precision Booth.

Later, Frank
Bartlein Barrels
 
Re: 338 LM Improved gain twist barrel

Frank

Nice to see you stopping by and adding your insight. My brother is using my SHOT ticket on Tuesday, but I will have it the rest of the week. I would be happy to meet and we can talk expensive tomatto stakes and the barrel business.

JeffVN