Has anyone tested this option, and if so was there any noticable difference between gain or normal barrel twist? I guess to me it just makes sense in my mind but I've been wrong plenty of times before.
- Thread starter Mattm8725
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Nat -Just if there was a big noticable difference really?
Badfinger - thanks I don't know how I've never seen that before!
Thanks guys I just watched the video I guess my only other question is why this isn't done more?
Badfinger - thanks I don't know how I've never seen that before!
Thanks guys I just watched the video I guess my only other question is why this isn't done more?
Litz tested the effects of different twist rates on velocity here. In his test, velocity correlated with the barrel twist at 1.33fps per inch of twist (between 1:12-1:8). I would assume the correlation would change depending on the bullet and caliber but it seems a difference of .5" twist is going to result in a very small difference in velocity. Litz's test does show a gain twist barrel increases velocity though, the 1:8 was at 2649fps and the 1:10-1:8.3 was 2656.
Frank, in a standard length barrel, let's say 24", would you say that the bullet is fully engraved to the rifling, that there is no slipping of the bullet at the end of the bullets travel in the barrel?
Frank, in a standard length barrel, let's say 24", would you say that the bullet is fully engraved to the rifling, that there is no slipping of the bullet at the end of the bullets travel in the barrel?
Twist and velocity have very little if anything to do with each other. Twist is about stability, length is about velocity
The idea Frank was talking about in his video was, the gain twist allowed a hotter load without deforming the bullet, is that what you got out of it?
I have a bunch of gain twist barrels, everything from small gains, 8.5 to 7.7 up to 13 to 5 in another. Currently, I have gain twists for 260, 6CM, and 338, the results are outstanding.
Gain twist done right work, Bartlien is gain twist done right. They forwarded the barrels to Hornady who tested pressure and I spoke to them about it. They (Hornady) found no negative effects and no pressure issues. There is no slipping or laying the rifling on the bullet, it is not adding extra grooves in the barrel or anything like that. It's much worst to over twist a barrel, it harms the bullet more so than using a gain twist. A gain twist solves the problem of pressure, speed, etc, by spinning the bullet at a more gradual rate vs jamming it hard right off the bat.
Gain Twist barrels work.
Gain twist done right work, Bartlien is gain twist done right. They forwarded the barrels to Hornady who tested pressure and I spoke to them about it. They (Hornady) found no negative effects and no pressure issues. There is no slipping or laying the rifling on the bullet, it is not adding extra grooves in the barrel or anything like that. It's much worst to over twist a barrel, it harms the bullet more so than using a gain twist. A gain twist solves the problem of pressure, speed, etc, by spinning the bullet at a more gradual rate vs jamming it hard right off the bat.
Gain Twist barrels work.
How does one identify how much gain is needed? And how does one also determine how slow or how fast to start/end? For example, if you determine the optimal twist rate for whatever bullets you want to use in X caliber is a 10 twist, does one do a difference of one? Start at 10.5 and end at 9.5? Etc.
This is very interesting info.
From Bartlein:
"For the most part, I would say there is no velocity gain in a gain twist barrel with the same load. What has been conveyed to us and it goes back to Popes 1st point is that shooters have noticed that they can run a slightly heavier powder charge vs. a shooter with a straight twist barrel. As the bullet is starting easier into the rifling my only guess is the pressure isn’t spiking as fast or is delaying the pressure curve. Hence forth they can get more velocity out of the gain twist barrel. I feel pressure is pressure and that the twist doesn’t have anything to do with pressure for the most part but my only guess is that the gain twist like I said earlier is delaying the pressure curve. So you don’t see problems as early like hard bolt lift etc"
"For the most part, I would say there is no velocity gain in a gain twist barrel with the same load. What has been conveyed to us and it goes back to Popes 1st point is that shooters have noticed that they can run a slightly heavier powder charge vs. a shooter with a straight twist barrel. As the bullet is starting easier into the rifling my only guess is the pressure isn’t spiking as fast or is delaying the pressure curve. Hence forth they can get more velocity out of the gain twist barrel. I feel pressure is pressure and that the twist doesn’t have anything to do with pressure for the most part but my only guess is that the gain twist like I said earlier is delaying the pressure curve. So you don’t see problems as early like hard bolt lift etc"
Maybe someone will do some testing on the gain twist idea, sure seems to make sense.
I started off very conservative, except for that 13-5 which was built for a specific bullet and was spec'd out by the designer. Otherwise, I think people can a bit more aggressive than I went.
For a 6.5 caliber, I would do an 8 to 7 twist,
For a 30 cal, I would do a 10 to 8,
Same for 338
The 6mm can go about 8.25 to 7.5
There are service rifle guys using aggressive twists, like 14 - 6 or something, they claim to use these twists because they can mix heavy and light bullets in the same competition at the same time. So for the short range stuff they go light and work up to 90gr heavies.
There is a school of thought that says you can over twist a barrel, or in their mind, you can't over twist one. But we see and have very good evidence you can, and the limiting factor is the jacket technology, and lead vs solid. A solid bullet can be over twisted, a jacketed bullet not nearly as much as they claim. You risk one of three outcomes, you damage the jacket and leak lead out like a pinwheel, or the entire bullet will come apart in the air. The other issue is, you shift the lead under the jacket and the bullet is out of balance. That gives people that odd flier, as it can be enough to throw the bullet off, or it can affect the BC, lowering it. It's like having excessive runout in the bullet/load.
For a 6.5 caliber, I would do an 8 to 7 twist,
For a 30 cal, I would do a 10 to 8,
Same for 338
The 6mm can go about 8.25 to 7.5
There are service rifle guys using aggressive twists, like 14 - 6 or something, they claim to use these twists because they can mix heavy and light bullets in the same competition at the same time. So for the short range stuff they go light and work up to 90gr heavies.
There is a school of thought that says you can over twist a barrel, or in their mind, you can't over twist one. But we see and have very good evidence you can, and the limiting factor is the jacket technology, and lead vs solid. A solid bullet can be over twisted, a jacketed bullet not nearly as much as they claim. You risk one of three outcomes, you damage the jacket and leak lead out like a pinwheel, or the entire bullet will come apart in the air. The other issue is, you shift the lead under the jacket and the bullet is out of balance. That gives people that odd flier, as it can be enough to throw the bullet off, or it can affect the BC, lowering it. It's like having excessive runout in the bullet/load.
Frank did that video quite a while back. Seemed like for awhile he (& others) were hot on the trail of LH gain twist advancement foe awhile. For the last year or so, perhaps longer, the subject seems to have vanished from these boards & I am wondering why. Has the technology of gain twist fallen out of favor? No one seems to discuss it any longer. The preponderance (if not all) of inventory I see from barrel makers appears to be RH twist. ELR doesn't seem to be favoring GT as far as I can see. For awhile it was a hot topic, seemed to make perfect sense & then discussions vanished. Are people moving toward GT or has it be shown to be not any more effective than a regular consistant rate of twist? Can anyone elaborate? As I'm still considering GT on a new barrel I'd sure like to be more knowledgeable on the topic.
I am the only one talking about it, the others are all happy to repeat the tired old thing.
Gain twists work, Bartlein sold a bunch, and a guy posted on FB about Warner Tools 6.5s using a LH Gain Twist he ordered.
I just haven't ordered any barrels in a while
Gain twists work, Bartlein sold a bunch, and a guy posted on FB about Warner Tools 6.5s using a LH Gain Twist he ordered.
I just haven't ordered any barrels in a while
Guess you found a good podcast topic.
What about barrel life expectancy? With out the slipping/skidding it seems to me you would get better barrel life? Frank would this stand to reason or am I off track?
You could also burn more powder with a gain twist before you start running into pressure issues so I'd think the difference might be very marginal for those who do run hot loads on GT barrels. Just some more food for thought.
My 6.5x47 gain twist 8-7 left twist..is the most accurate rifle i got..really stable SD shot this card sideways at 100yards two bullets left over..either the first try split or tje second onei was aiming on indicator..its laser!!! I would definitely do it again
The potential velocity advantage of GT it seems to me is minimal compared to the biggest advantage of GT which, IMO would be for use in ELR as a faster twist should translate to a more stable bullet for a longer period of flight time thus extending the distance & time before transonic velocities start destabilizing the bullet, especially the very long nosed solids. It just makes sense that achieving a faster spin rate than would ordinairly be possible without seriously deforming the bullet and/or destroying the jacket would be very advantageous shooting at extreme distances. Yet I don't think the current major players in that game seem to be pursuing GT technology. There seems to be alot going on in bullet & case design but not much or anything on barrels (other than they continue to get longer). I just don't understand the apparent reluctance to develop this & take advantage of the obvious benefits considering all the other advances people are working on & striving for in the world of extreme distance.
The problem is, as usual, there is no enough hard data to draw any valid and technical conclusion most especially when it comes to transonic and beyond. I don't buy the argument of a bullet going thru any better with a GT barrel.
Gain Twist is the answer to move barrel technology to the next level.
Unfortunately, the little bit I talk about is not enough to push the manufacturers further. Groups are testing barrels by overtwisting stuff and looking at the transonic results, but very few if anyone is playing with GT stuff. I promote it here and there when I grab a new one. But otherwise, it's just me doing the talking here.
There is a lot of talk about fast twist rates easing the transition to transonic, but like I said, you become subject to the bullet maker on a lot of levels. None of them good. They are not QC'ing every bullet so it doesn't take much to have a defect a fast twist barrel will exploit. Because the bullet has to be shot, they don't follow up. But we know it is happening, and we have seen whole lot bullet recalls in the past. I know some companies are talking about jacket tech, thickening up the jackets because people want to over twist. But you can over twist using a GT barrel and not have the negative.
The bullet is not skidding or laying over multiple grooves, it does not work that way. It's progressive or gradual and not some big change in width, or anything.
It works, it's more forgiving, it's better for a variety of bullet weighs, the advantages are numerous.
Going back to Pope and his rifles, part of the problem is mass production. He was very slow and hand rifled his barrels. He was using LH GT Barrels back at the turn of the 20th Century. He was a Silohoutte shooter, so positional was important and he was absolutely convinced a Right Handed Shooter should be using a LH GT Barrel. His score spoke for themselves, I think it took like 50 years to beat his scores. Once companies went to mass-produced machines to make this stuff, it all went right-handed with standard twist rates but the machines were not capable of doing it until now. So the Tech Died until Bartlein with their Computer Controlled Rifling.
For ELR it is smarter unfortunately not enough guys are hip to this
Unfortunately, the little bit I talk about is not enough to push the manufacturers further. Groups are testing barrels by overtwisting stuff and looking at the transonic results, but very few if anyone is playing with GT stuff. I promote it here and there when I grab a new one. But otherwise, it's just me doing the talking here.
There is a lot of talk about fast twist rates easing the transition to transonic, but like I said, you become subject to the bullet maker on a lot of levels. None of them good. They are not QC'ing every bullet so it doesn't take much to have a defect a fast twist barrel will exploit. Because the bullet has to be shot, they don't follow up. But we know it is happening, and we have seen whole lot bullet recalls in the past. I know some companies are talking about jacket tech, thickening up the jackets because people want to over twist. But you can over twist using a GT barrel and not have the negative.
The bullet is not skidding or laying over multiple grooves, it does not work that way. It's progressive or gradual and not some big change in width, or anything.
It works, it's more forgiving, it's better for a variety of bullet weighs, the advantages are numerous.
Going back to Pope and his rifles, part of the problem is mass production. He was very slow and hand rifled his barrels. He was using LH GT Barrels back at the turn of the 20th Century. He was a Silohoutte shooter, so positional was important and he was absolutely convinced a Right Handed Shooter should be using a LH GT Barrel. His score spoke for themselves, I think it took like 50 years to beat his scores. Once companies went to mass-produced machines to make this stuff, it all went right-handed with standard twist rates but the machines were not capable of doing it until now. So the Tech Died until Bartlein with their Computer Controlled Rifling.
For ELR it is smarter unfortunately not enough guys are hip to this
Frank, not having special-ordered a barrel before, I'm not familiar with the best way of going about it. I guess an order directly through Bartlein would be best? I've read enough about these that I'm ready to try it on my next barrel, but given lead times for specialty barrels, I need to do it sooner rather than later.
I just placed another GT and bartlein says "i would stick 3/4 twist gain".so i went with 8.25-7.5
What kind of lead time did they quote you?
4-6 months
Thanks everyone for your input. This has been really informative. I definitely think my next barrel is gonna be a LH GT!
I have used the Bartlein Gain twist 1-13 to 1-6.5, in a .223 service rifle, gunsmithed by Joe Carlos for the last two years, they shoot very well. I use it for NRA service rifle competition and in 2016 & 2017 I won the Civilian Service Rifle Championship at the NRA Nationals. I have had good luck with the 90 grain Sierras.
The 3/4 twist gain, what caliber and weight range where they recommending that for?
Tagging in
Ask frank...press #2 when autmated answers it will take you direct or brian..im getting another 6.5
The 30 cal should be here in a week or two..its 8.5-8 twist to run new smk 230s for 300norma cip
Just a thought would using a GT barrel add more life to the barrel,if you have a overbore calibers.
There is plenty of data, the service rifle guys are using it, Hornady tested them, and Pope from the turn of the century swore by them.
The data is not complete, and it’s scattered around, but there is data.
Guys have been quietly using them for a while now. They are just harder to make for a typical barrel maker so they avoid the conversation, if not rightly dismiss it because they can’t make them like Bartlein does. That why it died, the original Pope barrels were hand made, once the process went to mass production at the turn of the century, it died offf because the machines to make barrels were not capable. Today with CNCs we can do it right.
At Shot my entire conversation with the team from Bartlein focused on GT. For no data that that was a lot of talking we did.
Just because few do it, doesn’t automatically dismiss it.
The data is not complete, and it’s scattered around, but there is data.
Guys have been quietly using them for a while now. They are just harder to make for a typical barrel maker so they avoid the conversation, if not rightly dismiss it because they can’t make them like Bartlein does. That why it died, the original Pope barrels were hand made, once the process went to mass production at the turn of the century, it died offf because the machines to make barrels were not capable. Today with CNCs we can do it right.
At Shot my entire conversation with the team from Bartlein focused on GT. For no data that that was a lot of talking we did.
Just because few do it, doesn’t automatically dismiss it.
Sure. I was 3rd last year at the 1,000 yard Nationals with a gain twist .223 from Bartlein. I was a long way from first, but a helluva lot further from last than I expected, so I'll take it.
The truth is that I am able to put in more go-fast-dust and stabilize a heavier bullet FASTER then I would without the gain twist. Hell, I only make it across the line at about 1,205 as it is.
In a TRULY limited cartridge like the .223, and in a TRULY limited barrel like a 20", trust me, you need ALL the help you can buy. Bartlein was willing to do that, where nobody else would.
Gain twist, to me, is not the sort of thing that is a WORLD changer, but it can be an edge if you need it. The only thing I would change on the next barrel would be to go more aggressive on the gain.
Signed: Krieger Fanboi (most of the time).
-Nate
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Oops. Mr. Frank beat me to the punch.
But yeah, I'm one of those Service Rifle guys. Only thing I didn't mention is that it is a 3/4 Minute (or better) upper with a 2.595" long stupid-MF-90 grain round. If you're not familiar, 2.260" is the "stop" on .223.
-Nate
But yeah, I'm one of those Service Rifle guys. Only thing I didn't mention is that it is a 3/4 Minute (or better) upper with a 2.595" long stupid-MF-90 grain round. If you're not familiar, 2.260" is the "stop" on .223.
-Nate
Nate, did you find an accuracy node at a higher velocity with the GT barrel vs non-GT barrel? It seems that for GT to be a benefit, there has to be a point where the bullet is being damaged before there is too much pressure.
Being that "high" velocity in these isn't very high, bullet damage is less critical. If it were a .22-250, maybe you only do a 7.0-6.5 Gain...but in .223, there are guys doing as much as 13.0-6.5 gain and doing fine.
As for the accuracy node, frankly, I was pressed for time. I'm not THAT impressed with the load I had, but it was less than 1/2 MOA vertical. I seriously doubt that the barrel was the problem. One main problem is 90-grain bullets...they are finicky little bitches, particularly in the little casing, and concentricity and SD can be not-awesome.
-Nate
As for the accuracy node, frankly, I was pressed for time. I'm not THAT impressed with the load I had, but it was less than 1/2 MOA vertical. I seriously doubt that the barrel was the problem. One main problem is 90-grain bullets...they are finicky little bitches, particularly in the little casing, and concentricity and SD can be not-awesome.
-Nate
Just seeing this thread....and I didn't read the whole thing....I'll give a little update. We did talk to Hornady at Shot Show. We are going to make a couple more pressure barrels for testing. These are going to be a dual port pressure barrels. One port will measure the chamber pressure like normal and a second port say approx. 6" in front of the chamber to see if the pressure drops faster in a GT barrel.
On one hand I will say for the most part twist has nothing to do with or should have any effect on the pressure at all.
The first two barrels we made we only did a normal chamber pressure port and this did confirm the the chamber pressure was no different. What we don't know at this time is what does the pressure do shortly in front of the chamber area. Does it drop off faster? From the chamber to about 6" in front of the chamber pressures are still pretty high and will slowly drop as you go towards the muzzle.
The reason for the testing is to prove if it does or not. Keep in mind to our knowledge no testing has been done like this in who knows how long!? Or if at all.
Hornady is going to do the testing at n/c and we are making the barrels at n/c to Hornady etc...so we all have to have a little patience etc...Hornady will work the testing into they're schedule when time permits. Those pressure sensors are approx. $3k each. Now throw in time, ammo, barrels, labor etc...
Also keep in mind it's not just one barrel they will be testing. Most likely we will make say 2 barrels in .308win. and 2 barrels in say 6.5CM. One of each barrel will be a standard straight twist and one of each barrel will be a gain twist. All of the barrels will have dual pressure ports. So there is a lot of data to collect and keep track of just for 4 barrels.
Why two different calibers and multiple barrels? We don't want to have a situation occur where we get data that says one thing and we take it for the gospel word etc....we want to rule out and and all variables.
Hope that all made sense!
Later, Frank
Bartlein Barrels
On one hand I will say for the most part twist has nothing to do with or should have any effect on the pressure at all.
The first two barrels we made we only did a normal chamber pressure port and this did confirm the the chamber pressure was no different. What we don't know at this time is what does the pressure do shortly in front of the chamber area. Does it drop off faster? From the chamber to about 6" in front of the chamber pressures are still pretty high and will slowly drop as you go towards the muzzle.
The reason for the testing is to prove if it does or not. Keep in mind to our knowledge no testing has been done like this in who knows how long!? Or if at all.
Hornady is going to do the testing at n/c and we are making the barrels at n/c to Hornady etc...so we all have to have a little patience etc...Hornady will work the testing into they're schedule when time permits. Those pressure sensors are approx. $3k each. Now throw in time, ammo, barrels, labor etc...
Also keep in mind it's not just one barrel they will be testing. Most likely we will make say 2 barrels in .308win. and 2 barrels in say 6.5CM. One of each barrel will be a standard straight twist and one of each barrel will be a gain twist. All of the barrels will have dual pressure ports. So there is a lot of data to collect and keep track of just for 4 barrels.
Why two different calibers and multiple barrels? We don't want to have a situation occur where we get data that says one thing and we take it for the gospel word etc....we want to rule out and and all variables.
Hope that all made sense!
Later, Frank
Bartlein Barrels
Gain Twist, Gain Twist, Gain Twist
sing it with me...
It's certainly smarter than guys trying to overspin stuff right off the bat while adding velocity... especially for the ELR guys why they are not the left-hand gain twist I have no idea, they are missing a huge opportunity to add velocity and spin without the drama. Not to mention most are now switching to solids so you can spin them even harder.
The conversation everyone avoids that Nate above alluded too is the BULLET.
The bullet is the weak link, talking jacketed bullets here. When you have a softer lead underneath and a thin jacket you seriously risk damaging the bullet or at least throwing it out of balance by shifting the lead under the jacket. It may not always rip or come apart, but it can and will deform. it's like having excessive runout on a long bullet, it's not gonna fly straight. Two things may or may not happen, you lose a bunch of BC because it's not flying right or it comes apart and never makes it to the target.
This is moving forward like Frank said above, and I am helping to lead the charge cause I have seen it work across multiple platforms, from 338 to 6mm I am running gain twist barrels.
sing it with me...
It's certainly smarter than guys trying to overspin stuff right off the bat while adding velocity... especially for the ELR guys why they are not the left-hand gain twist I have no idea, they are missing a huge opportunity to add velocity and spin without the drama. Not to mention most are now switching to solids so you can spin them even harder.
The conversation everyone avoids that Nate above alluded too is the BULLET.
The bullet is the weak link, talking jacketed bullets here. When you have a softer lead underneath and a thin jacket you seriously risk damaging the bullet or at least throwing it out of balance by shifting the lead under the jacket. It may not always rip or come apart, but it can and will deform. it's like having excessive runout on a long bullet, it's not gonna fly straight. Two things may or may not happen, you lose a bunch of BC because it's not flying right or it comes apart and never makes it to the target.
This is moving forward like Frank said above, and I am helping to lead the charge cause I have seen it work across multiple platforms, from 338 to 6mm I am running gain twist barrels.
Thank you Frank and Frank, I mean Frank G. and Frank G.
Frank Green, I do know that I will be ordering a LH gain twist .338 barrel from you this year, as soon as I get some other stuff out of the way. Maybe two if I can 'twist' my shooting buddy's arm to go in at the same time. Once I get close, I'll call and discuss it with you first.
Frank Green, I do know that I will be ordering a LH gain twist .338 barrel from you this year, as soon as I get some other stuff out of the way. Maybe two if I can 'twist' my shooting buddy's arm to go in at the same time. Once I get close, I'll call and discuss it with you first.
Frank Green,
Assuming a GT barrel reduces resistance to the accelerative force on the bullet, shouldn't the initial pressure be lower in a GT vs non-GT barrel?
Assuming a GT barrel reduces resistance to the accelerative force on the bullet, shouldn't the initial pressure be lower in a GT vs non-GT barrel?
So if Im understanding the physics here correctly, the rotational acceleration/impulse on the bullet is delayed and is more gradual than slamming a slow bullet under high pressure into the lands and into immediately fast rotation?
Either of the Franks, or any other savants, please confirm the following
-Pressure peaks are identical between barrel types
-Muzzle velocity at barrel tip/exit doesn't change
Has there been any research done, that can be talked about in a forum, around progressive rifling depth or rifling shapes?
Lastly, I agree that the weak link here is the bullet. They are primitive at best. I'd love to see a tight tolerance, bimetallic bullet with a high temp polymer/ceramic composite jacket...there I go again...thinking on my own without supervision...
I know bench rest dweebs who are measuring jacket thickness and rotational balance who swear by this sorting process...are we doomed to the same fate?
Either of the Franks, or any other savants, please confirm the following
-Pressure peaks are identical between barrel types
-Muzzle velocity at barrel tip/exit doesn't change
Has there been any research done, that can be talked about in a forum, around progressive rifling depth or rifling shapes?
Lastly, I agree that the weak link here is the bullet. They are primitive at best. I'd love to see a tight tolerance, bimetallic bullet with a high temp polymer/ceramic composite jacket...there I go again...thinking on my own without supervision...
I know bench rest dweebs who are measuring jacket thickness and rotational balance who swear by this sorting process...are we doomed to the same fate?
Again what I've always been taught is that the twist for the most part has no real bearing on chamber pressure per say. Just sticking with a .308 barrel the difference in a 12 twist vs. a 10 twist is basically non existent.
Bore and groove sizes effect pressures a lot. Groove size has a bigger impact then changing the bore size but anytime you start changing the total surface area of the bore you effect pressures. That's why when you look at say Saami drawings they not only call out the spec's of the bore but there is a note of what the total surface area of the bore cannot be under.
Same goes for the chamber. You start shortening up the throat, tightening up the diameter etc...you will effect pressures and in turn effect velocities.
Most people don't even think about bore and groove sizes and the chamber when they start saying this brand barrel or that brand barrel is faster or slower etc....you want to start comparing brand X to brand Y you better know the bore and groove sizes to the 4th decimal place. Don't just say well that both barrels are .308. Same goes for chambers....one guys is running a standard .308win chamber and the next guy has a .308palma chamber in his gun.
Another good example we witnessed about a year ago was a company had some test barrels from another maker as well as ours. All of the barrels where suppose to be made to the Saami spec. for that caliber. Our barrels with the reference ammunition came in at spec. for velocities and pressures. Our barrels where with in 10fps. velocity wise (on three barrels). The other brand barrels had pressures that where running 8k psi higher and velocities where up 150-200fps. They could not figure out what was going on. They called and asked if we had any ideas. I asked what are the bore and groove specs. on the other brand of barrels. They didn't know as they didn't get inspection reports with the barrels. So they had the barrels checked and the bore and grooves where .0005" under the min. spec. So that small of a change has a big impact.
Going back to your question.....in theory the GT should offer less resistance and or if you want to say help the bullet start easier and one would think help lower pressure. From what we've seen so far is that chamber pressure is still chamber pressure and haven't seen a difference. Hornady tested .308win. and 6.5CM in pressure test barrels. The GT was from 12 to 8 on each of them. What we need to do next is rerun the test and like I said have the 2nd pressure port approx. 6" from the breech end. If it is going to reduce pressure or what I would guess is the pressure spike curve/delay the curve this is what we need to find out and see what is happening.
We have to have the normal chamber pressure port so we know we are getting apples and apples here....as well as measure the pressure 6" from the breech end. We to compare the pressures to the straight twist barrel and the GT barrels.
Everything will be the same in regards to chamber reamer spec. (same chamber reamer used) bore and groove tolerances, lot of ammo being used etc...the only change is the rifling twist from a straight conventional twist and the GT.
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Not sure what you are asking on your first question. Pressure peaks are identical between barrel types? Read my previous post to this and see if it answers your question.
Research on rifling types.....for the most part the style of rifling...5R, standard 4 groove, 6 groove, 3 groove etc...I don't see or have seen any difference in regards to effecting pressure. This data comes from ammunition pressure test barrels and the testing has been done. Rifling depth does effect pressures. Again see my previous post and it does have a big impact. GT vs. straight twist is what is being tested right now. I don't know when or if ever it's been checked/tested.
Bullets can and are a variable. Not just barrels and chambers. Jacket thickness has a bearing on bullet failure in conjunction with velocities and the spin/rpm of the bullet.
Same bullet velocity at different twist rates.
2700fps. with a 12 twist barrel you are getting 162,000 rpm.
2700fps with a 8 twist barrel you are getting 243,000 rpm.
2700fps. with a 6.5 twist barrel and you are getting 299,076 rpm.
The forumla is FPS x 720 divide by twist = RPM
Now throw in bullets on the diameter. One lot of bullets measures right at the min. spec. lets say of .3080". You get another lot that measures .3084". You run both lots thru the same barrel. Lets say the barrel has a groove size of right at .3080". With all things being equal, powder, primer round count on the barrel....the fatter bullets should make your pressures higher. Again though there are variables that we don't know and cannot necessarily measure. This was just recently pointed out to me by a bullet/ammo maker. They feel jacket hardness varies but it is so hard to measure the jacket hardness. In theory they feel it can have an effect on bullet failure etc....but again it's so hard to measure.
Yes the BR guys are anal and for a specific reason. They measure jacket thickness for consistency, bullet run out etc....they know that the more consistent the bullets are, powder, barrels etc....the more consistent the guns will be and the smaller the groups are. Keep in mind they are trying for the perfect one hole 5 and 10 shot groups. Mark here in the shop/office is primarily a BR shooter (just got him into F class a year ago and he likes it). He makes his own bullets and just set another world record that got confirmed a month ago. 10 shots at 100 yards and the group measured .104". He knows more about bullets then I do. Also he doesn't cherry pick his barrels etc...last year we only made him two barrels. One for his light gun and one for his rail gun.
Later, Frank
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