Promised S. ELR Bullet CFD

[bohem]

I figured I would start a new thread rather than stir up the shit-storm which has brewed in the 5,000m thread and what started in the GSC 414 G2 thread.

In the 5km thread another member asked me to do a quick check on a bullet design that he'd rolled together. I agreed to put it through the computer models that Ply1951Guy and I (mostly PlyGuy) have come up with in the past several months of research and development work.

Groper,

Here's the first IGES file that you sent. I asked Ply1951Guy to run it through the CFD models and do some initial investigation on it. This is not an entire, start to finish, analysis but rather a proof of concept and something to create pretty pictures. The computing system takes time to run each model and we didn't want to jeopardize our research time line through running multiple models and full analysis for what has turned into an online bickering contest. I promised we'd take a quick look, I really don't feel like getting dragged into the fighting over who said/did what. To all those reading, please take the analysis for what it's worth, please avoid from all the name calling, smack talking BS. I started a new thread to avoid the black cloud following those other ones, I appreciate the hard work going on to push the envelope in the "real" world. We would both like to continue with our research and push the computational envelope as well.

What we can do currently:

CFD Analysis that has been correlated to less than 1% difference with Mr. Bryan Litz's radar data on several commercially available bullets. This has been leveraged to analyze some research work and investigation into several common "high level" questions in bullet flight theory for small arms munitions. We are currently able to predict, with a high degree of certainty:

Overall Drag and Drag Coefficients
Various Ballistic Coefficients
Center of Pressure Location
Magnus Moments
Overturning Moments
Precession Rate
Pitching/Yawing Moments
Shock Wave formation
Driving Band aerodynamic behavior
Gyroscopic stability based on aerodynamic properties, not empirical Miller Stability

We are currently working on:

Dynamic Stability
Transsonic Stability Prediction

In general our models are run at a number of various velocities and various orientations needed to calculate the stability predictions. For the sake of time, as I mentioned above, only 1 simulation point was run for the bullet model that you sent over. Again, not a slight towards anyone here, but neither myself or Francis want to be involved with the internet bickering. I almost didn't do this work due to the fighting going on over the topics, but I know I promised that we would so here's the results.

This bullet was run at:

Mach 2.5 = 2815 fps @ Standard Temperature and Pressure (STP) Freestream Velocity
Incidence angle = 0*
14.5mm projectile, 1601 grains appx. weight

<span style="font-weight: bold">Img removed for upload space</span>

The total drag on the shape at Mach 2.5 is appx 22 Newtons

Based upon the 1600.85gr bullet weight and other physical parameters this translates to:

G1 BC = 1.215 +/-1% @ M2.5
G7 BC = 0.564 +/-1% @ M2.5

Obviously there is a lot more work involved to predict gyroscopic/dynamic stability @ the muzzle, average ballistic coefficient over flight regime, transsonic stability downrange, etc. To do this would have taken approximately 3 weeks of work on our part due to the solution times for each model.

If anyone has additional technical questions either of us will evaluate how much information that we have and are willing to divulge at this point and get back to them. Please be understanding that this approach is very new and the tools used are highly proprietary, when we are ready to go public it will be in the form of Research Journals and we'll make an announcement on the forum. Potentially we will be offering bullets and/or analysis to bullet makers for high confidence development data before real projectiles are ever fired in test.

Thanks.

 

[jrob300]

Re: Promised S. ELR Bullet CFD

Josh, Groper,

It has been questioned in another thread (if I understood the intent) if this is actually a design capable of being spin stabilized. Again, please keep to the facts. I have no dog in this fight and am simply here to learn.

I too appreciate the groundbreaking work going on in this arena and would like to see collaboration instead of bickering. I'm just curious if this is a viable design or just a pipedream before we waste too much time on discussion.

Gentlemen?

John

 

[bohem]

Re: Promised S. ELR Bullet CFD

John-

There is a reasonable chance that this bullet it viable. Without getting ahead of myself there are some things in it that strike me as being "issues" and in a subsequent email, Groper made a comment that he suspected there might be an issue there as well. So I'm sure when he sees this plot it will validate some of his thoughts, it may raise more questions than it answers, but that's another story.

 

[karagias]

Re: Promised S. ELR Bullet CFD

Bohem and Plyguy,

F*!king Awesome!!!

Ted

 

[bohem]

Re: Promised S. ELR Bullet CFD

Thank you.

 

[BryanLitz]

Re: Promised S. ELR Bullet CFD

Interesting.

Can you remind me what CFD code you're using? It's impressive that you got within 1% of measured drag values. Did the CFD software achieve this by default, or did you have to tweak it to get it to match the measured data?

As for the design, just looking at it, I have a hunch it would need a radical twist rate to stabilize if it's even possible. However that's not backed up by anything but a hunch so don't be discouraged. It does have the 'large caliber' scaling effects working in it's favor. Larger caliber bullets are easier to spin stabilize than smaller calibers.

-Bryan

 

[jrob300]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">Larger caliber bullets are easier to spin stabilize than smaller calibers. </div></div>

Bryan,

I'd suspected that by just observing which bullets have fairly high BC's. But is that curve linear? At the risk of a thread derail, I've noticed very high BC .338's, but it seems to drop off quite a bit for .30 cal and interestingly goes back up for 7mm. Is this marketing or capability driven? Have we seen the best to be offered in the .30 cal world in a mass produced bullet?

John

<span style="font-weight: bold">Edit</span>: You can just PM me so we don't stomp around in Bohem's thread.

 

[bohem]

Re: Promised S. ELR Bullet CFD

Bryan-

I've asked Francis to address those questions more. The CFD code is not a released code, it was a custom written setup that requires some hoops to be jumped in order to run. The initial "first shot" at the problem yielded results around 2% (the initial data being that G7 Std shape I posted in the "Trace" thread) and since then the models have evolved to get closer and closer.

 

[BryanLitz]

Re: Promised S. ELR Bullet CFD

John,

It's not perfectly linear, but not far off. The plot on the next-to-last page of this article should address your question:
http://www.appliedballisticsllc.com/index_files/Understanding_part1.pdf

Looking at it from the bullets perspective, the twist rate is better considered in 'calibers per turn' more than inches per turn.

For example,
a 1:7" twist .224 barrel spins bullets at 7/.224 = 31.3 calibers per turn.
Likewise, a 1:8 twist .244 barrel is 32.8 calibers per turn.
A 1:9" twist 7mm is 31.7 calibers per turn
A 1:10" twist .30 caliber barrel is 32.47 cal/turn
and a 1:11" twist .338 is 32.5 cal/turn

all of the above twists (1:7" thru 1:11") are essentially the same twist for their respective calibers, all equaling between 31.3 and 32.8 cal/turn.

To your question, a 1:10" twist .338 barrel is proportionally very fast. It would be like a 1:9" twist .308. But since the 1:10" is thought of as 'common' for .338, we're able to make very long bullets to work with that twist (see the Berger 300 grain Hybrid).

Conversely, 1:10" is also a common twist for .277 caliber. In this smaller caliber, 1:10" is actually quite slow (36.1 cal/turn) which is why there are few options for long 'n heavy high BC 270 bullets.

.308 is an interesting one. Despite how common the adequate 1:10" twist barrel is, there are very few (almost no) good .308 bullets scaled to take advantage of that twist. In other words, the 7mm and .338 bullets are taking full advantage of the available twists, but the .308 is not. Here's an article to that effect:
http://www.appliedballisticsllc.com/index_files/30cal_fullVersion.pdf

I happen to know of one bullet maker who's currently working to optimize properly scaled heavy bullets for the .30 caliber.

-Bryan

 

[bohem]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">John,

It's not perfectly linear, but not far off. The plot on the next-to-last page of this article should address your question:
http://www.appliedballisticsllc.com/index_files/Understanding_part1.pdf

Looking at it from the bullets perspective, the twist rate is better considered in 'calibers per turn' more than inches per turn.

For example,
a 1:7" twist .224 barrel spins bullets at 7/.224 = 31.3 calibers per turn.
Likewise, a 1:8 twist .244 barrel is 32.8 calibers per turn.
A 1:9" twist 7mm is 31.7 calibers per turn
A 1:10" twist .30 caliber barrel is 32.47 cal/turn
and a 1:11" twist .338 is 32.5 cal/turn

all of the above twists (1:7" thru 1:11") are essentially the same twist for their respective calibers, all equaling between 31.3 and 32.8 cal/turn.

To your question, a 1:10" twist .338 barrel is proportionally very fast. It would be like a 1:9" twist .308. But since the 1:10" is thought of as 'common' for .338, we're able to make very long bullets to work with that twist (see the Berger 300 grain Hybrid).

Conversely, 1:10" is also a common twist for .277 caliber. In this smaller caliber, 1:10" is actually quite slow (36.1 cal/turn) which is why there are few options for long 'n heavy high BC 270 bullets.

.308 is an interesting one. Despite how common the adequate 1:10" twist barrel is, there are very few (almost no) good .308 bullets scaled to take advantage of that twist. In other words, the 7mm and .338 bullets are taking full advantage of the available twists, but the .308 is not. Here's an article to that effect:
http://www.appliedballisticsllc.com/index_files/30cal_fullVersion.pdf
<span style="font-weight: bold">
I happen to know of one bullet maker who's currently working to optimize properly scaled heavy bullets for the .30 caliber.

</span>

-Bryan </div></div>

Very nice to hear this

 

[jrob300]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">John,

It's not perfectly linear, but not far off. The plot on the next-to-last page of this article should address your question:
http://www.appliedballisticsllc.com/index_files/Understanding_part1.pdf

Looking at it from the bullets perspective, the twist rate is better considered in 'calibers per turn' more than inches per turn.

For example,
a 1:7" twist .224 barrel spins bullets at 7/.224 = 31.3 calibers per turn.
Likewise, a 1:8 twist .244 barrel is 32.8 calibers per turn.
A 1:9" twist 7mm is 31.7 calibers per turn
A 1:10" twist .30 caliber barrel is 32.47 cal/turn
and a 1:11" twist .338 is 32.5 cal/turn

all of the above twists (1:7" thru 1:11") are essentially the same twist for their respective calibers, all equaling between 31.3 and 32.8 cal/turn.

To your question, a 1:10" twist .338 barrel is proportionally very fast. It would be like a 1:9" twist .308. But since the 1:10" is thought of as 'common' for .338, we're able to make very long bullets to work with that twist (see the Berger 300 grain Hybrid).

Conversely, 1:10" is also a common twist for .277 caliber. In this smaller caliber, 1:10" is actually quite slow (36.1 cal/turn) which is why there are few options for long 'n heavy high BC 270 bullets.

.308 is an interesting one. Despite how common the adequate 1:10" twist barrel is, there are very few (almost no) good .308 bullets scaled to take advantage of that twist. In other words, the 7mm and .338 bullets are taking full advantage of the available twists, but the .308 is not. Here's an article to that effect:
http://www.appliedballisticsllc.com/index_files/30cal_fullVersion.pdf
<span style="font-weight: bold">
I happen to know of one bullet maker who's currently working to optimize properly scaled heavy bullets for the .30 caliber.

</span>

-Bryan </div></div>

Very nice to hear this

</div></div>

That is VERY good to hear. Thanks for the explanation, Bryan.

John

 

[ply1951guy]

Re: Promised S. ELR Bullet CFD

Bryan,

The CFD software is actually pretty good all by itself, you just need an educated user to do more than just push some buttons. However, as Bob McCoy always used to say, "Garbage in-Garbage out." Making sure that the geometries are correct, the boundary conditions are accurate, and the mesh is 'adequate,' are all very important to do. (The meshing issues can be a whole other discussion by itself.) When you feed the model good information, then you can get out values that are very close to those published in your book. Yes, it takes a lot of pre-work and it is time consuming, but all the work you put in makes the answers that much better.

Just as a comment for everyone else, you should read all of Bryan's articles he has posted on his website. There is a whole lot of very good info in them.

Also, just to clarify, the bullet pictured is not our (Bohem and myself) design. It is a design that 'groper' posted in another thread, and we just did the CFD.

Thanks, Ted.

 

[cav has been]

Re: Promised S. ELR Bullet CFD

Bohem, Bryan, Ply, John, et al, Thanks for sharing! Even though some of this is over my head I appreciate your work and your sharing of results and opinions. Some of us welcome the chance to learn from those of you with a greater understanding of things ballistic. Please continue to share. May the naysayers post elsewhere.

 

[groper]

Re: Promised S. ELR Bullet CFD

Nice work guys...

Yep, lots of problems with that projectile, as one would expect from something that was thrown together in 20mins... it does show however, that when your working with 1600grains its not hard to get impressive BC numbers!

Couple things tho... Would you care to elaborate on the analysis, what it is showing us, and explain how it can highlight the problem areas in the design for the purposes of trouble shooting?

Can you model what the projectile would have looked like after it left the muzzle with the rifling engraving, or would we need to do another CAD drawing of the projectile, engraving included in the drawing to model it?

See in reality with a projectile like this, the driving bands would not have square edges but radius' from the cutting tool and then tumbling after machining which rounds them off even more. The moly coating fillets these area even more and fills the gaps between bands etc... you end up with a smoother surface that what is shown here strictly for machining purposes.

It is interesting however, to see the turbulence from the drive bands totally ruining the flow over the boattail! How would you describe the flow over the nose cone tho

 

[Jeffvn]

Re: Promised S. ELR Bullet CFD

I too wonder what kind of twist would be required to stalize this projectile.

Although I personally would prefer one in .338 or .375, but I am glad to see the efforts to push the edge of the envelope in this area.

Keep it up guys.


JeffVN

 

[jrob300]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: groper</div><div class="ubbcode-body">It is interesting however, to see the turbulence from the drive bands totally ruining the flow over the boattail! </div></div>

I noticed this and wondered at what point do drive bands become an advantage over conventional bullet design?

John

 

[bohem]

Re: Promised S. ELR Bullet CFD

Groper-

Some of the more technical details are something to address via PM, so we'll talk more later.

The nose flow looks good, the driving bands and boat tail (in part due to the driving bands) have problems. There is a lot of "extra" shock waves produced from the driving bands. Like you mentioned, tumbling, engraving, moly, handling, tool shape will all make a difference to the flow behavior.



Jeff,

This bullet was run quickly from a request that came from another thread. A 338 bullet would be much more useful than a 570 caliber Destructive Device projectile, but that was the request.

Francis and I have done a lot of investigation in things from 6.5 up through 338's and have some promising designs that are stable in a range of barrel twists. As I understand it, Groper has been working on some 375's but Francis and I have no affiliation with him beyond checking on this bullet quickly, so he can decide to release whatever details he'd like to.

John-

Driving bands and engraving marks affect the bullets in small ways at high speeds, at low speeds (approaching Mach 1) they make larger and different problems.

 

[groper]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeffvn</div><div class="ubbcode-body">I too wonder what kind of twist would be required to stalize this projectile.

Although I personally would prefer one in .338 or .375, but I am glad to see the efforts to push the edge of the envelope in this area.

Keep it up guys.


JeffVN </div></div>

A very tight twist, 22calibers/turn. or 1:13in. Thats equivalent of 7.5twist in a .338cal. i had issues with this much twist in such a powerful caliber and the recoil/torque ramifications this would introduce, but thats what i was given to work with so went ahead and drew that 7 calibers long. It would be difficult to make a copper projectile around 1600grains and not be this long. Mass could be retained and reduce its length slightly by using a shorter nose cone with reduced fineness ration at the expense of increased nose drag, doing this also has some added stability benefit. You can see this change in the GS .375 414gr mk1 compared to the mk2 btw... Another way to reduce drag over the drive bands is to use a larger diameter nose cone, closer to the OD of the drive bands so the drive bands are in the "shadow" of the nose flow and the base of the nose cone effectively becomes the first band. however this is at the expense of increased initial engraving pressure... all things worth considering from a design viewpoint and its intended purpose

Advantages of drive bands include allow much lower engraving pressures and barrel friction, and therefore more velocity from the same mass projectile given more powder to reach the same chamber pressure. The velocity increase in a way, offsets the losses in drag and when the bands are designed properly, they contribute very little to aerodynamic drag anyway.

It was nice to physically see, through this CFD analysis, what happens when they are NOT done correctly and the effect they can cause...

And to clarify, this was not one of my 'designs' but rather a simple 'drawing' thrown together in 20mins, mainly for the purposes of scale and dimensions of a 1600gr 14.5mm projectile. My actual 'designs' that have taken countless hours of work, look nothing like this with the only similarity being the nose profile. I have no desire to give away these designs or even show a picture on the WWW just yet, soon tho

 

[Jeffvn]

Re: Promised S. ELR Bullet CFD

Groper

I hhave one of two .338 barrels in the US that has an exit twist of 5.4" - that is NOT a typo - 5.4" at the crown. The torque and twist from my 338LM Imporved eats every jacked bullet that I have tested so far (I remove the muzzle break and test the jacketed bullets.. 300 grain smk toast, same for Lapua 300 grainers.

I bought the barrel to test some bullets for another bullet manufacturer. I just sold the other 338 Gain twist to another shooter that is here oin the Hide pretty often.

I can spin your pills fast enough to stablize them...

Jeffvn

 

[Augustus]

Re: Promised S. ELR Bullet CFD

I was surprised to see a BC in the 1.2 range on the 7 cal 1600 gr projectile. The 7 cal .375 ZA 420 gr. has a REAL G1 BC of 1.2+. Its little brother the 6.5 cal 400 gr has a drop measured average BC over the distance of 2560 yds of 1.025. At shorter distances it is around 1.1. Anyway I would have expected a bullet weighing 1600 gr. with similar shape would have a much higher BC.

 

[ply1951guy]

Re: Promised S. ELR Bullet CFD

Jeffvn,

You need to contact either Bohem or myself about your 338 needs. I knew Bartlein made barrels with that aggressive gain twist, but I did not know that they have only made two of them. We have been looking for someone with this barrel for quite some time, and the fact that only two exist explains to me why we were having such a hard time finding you. We need to talk about this offline, send myself or Bohem a PM. We already have exactly what you are looking for.

 

[bohem]

Re: Promised S. ELR Bullet CFD

Augustus-

The bullet you see above has issues in the driving bands and the tail section. It is also only being run at 1 speed, Mach 2.5

To understand the actual BC going on it needs to be run at a number of velocities and the numbers are then compared to the various G-standards to calculate the best "fit" to a curve.

The drag on this bullet is very high, 22N. As the driving bands pull kinetic energy out to feed the secondary shock behavior that they are generating it is driving the overall drag behavior up quickly, which kills the BC.

 

[Augustus]

Re: Promised S. ELR Bullet CFD

The ZA bullets also have drive bands and still have the posted BCs. Anyway I have the other 5.2 twist 338 barrel. I can chamber it for a 338 Edge or a 338/408. I also have a 6.5 twist 375 barrel and will have a 5.5 375 in the next mo. or so. If I can be of help let me know.

 

[bohem]

Re: Promised S. ELR Bullet CFD

Driving bands with certain geometry are still very good, this configuration above just happens to show issues. That's all that I meant by it, not that driving bands in general are miserable. I don't doubt that the ZA series have BC's in line with advertisement, that wasn't my intent if that's how it came across.

I spoke to Jeff earlier, we're formulating a plan to take advantage of that sexy gain twist you guys have.

 

[Augustus]

Re: Promised S. ELR Bullet CFD

OK great, I look foward to seeing what you have come up with.

 

[Bluejazz]

Re: Promised S. ELR Bullet CFD

Bohem,
while most of this thread is over my head technically, I appreciate all the work that you and Groper have put into this designs. I enjoy reading these type of threads for some reason. Maybe because it is cutting edge and I can learn something along the way. I have not read the 5km thread that you reference, but will try and find it. While this type of rifle might be more than I would want or need I wish you and Groper best of luck in your endeavor with this project.
I will continue to follow this thread with interest.
Groper,
by the way, I am known as Trueblue at LRH site, and thought your 375 was an awesome rifle.

 

[jrob300]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bluejazz</div><div class="ubbcode-body">I have not read the 5km thread that you reference, but will try and find it. </div></div>

You will need popcorn and an adult libation.

John

 

[Dogtown]

Re: Promised S. ELR Bullet CFD

Ah, CFD is so easy when you only have 2 dimensions

 

[bohem]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dogtown</div><div class="ubbcode-body">Ah, CFD is so easy when you only have 2 dimensions

</div></div>

You can't do the job in 2D... Above is a 2D slice of a 4D simulation (steady state, planar slice in a model capable of transient 3D)

 

[Bluejazz]

Re: Promised S. ELR Bullet CFD

Thanks for the headsup on the popcorn. I ended up eating a bag of crackers and enjoying a nice Reisling wine. The wine was needed after 7 pages of that thread.
I do have a question on the bullet design in this thread thou. Do the bands cause more barrel fouling?

 

[groper]

Re: Promised S. ELR Bullet CFD

No, bands generally do not cause more fouling...

My designs do not call for super fast barrel twist rates, which is one of the more appealing aspects of my conceptual designs... most people will be able to use a super high BC bullet from their existing barrel they shoot jacketed bullets from. My main focus has always been on stability as everything else follows from there. If you have more stability to work with, you can make a bullet longer, heavier and therefore more BC potential, from any given twist rate barrel... make sense? I currently have design models for 338cal in 1:9-10twists, 375cal in 1:9-10 and special one for 1:8twists, presently working on 30cal 1:10twist. All versions in both hollow point and solid. I dont really see any point in working on any caliber less than 30cal at this point, as they will be too expensive for that market to tolerate. The machining involved in these designs has many more steps and soaks up alot more machine time than a typical banded VLD projectile. ill look into it if the interest is there however...

 

[Jeffvn]

Re: Promised S. ELR Bullet CFD

Groper

I'll speak for myself, if someone can come up with a higher than existing BC pill in 6mm (Berger and Tubbs 115s), 6.5 (Berger or JLK 140s rule this space), or 7mm (Berger 180 is king of the hill), I think you could potentially sell as many as you can make, if you can get the price to a reasonable volume level. I think you can justify a premium price if you can show a significant (10% BC gain minimum) BC gain.

Here is why I think so. The vast majority of shooters are confined to fairly short ranges or swhooting spaces. If my memory is working, there are fewer then 100 1,000 yard ranges in the United States, not counting the various military bases. Most ranges that I have seen or even read about have caliber limitations. My old range in Houston, prohibits 338 LM and anything bigger then a 338 LM or built off of a .338LM case; my current range in Nevada has a 50 BMG and 50 BMG case ban, but is looking to change that to include the newest ultra-long range cartridges like 408 and 375 CheyTac. As a result, I suspect you'll get lots of nibbles on a higher then currently available BC pill. My desire is for a high BC 6mm and 7mm pill; especailly if you can get it stable from a "normal" twist barrel, say 7.5" twist in 6mm and 8.5 or 9.0 twist in 7mm. I would use them for F-Class purposes 6mm for 600 yard, 7mm for 1,000 yard) and shooting in the desert out to and beyond a mile (I already do that with my current 7WSM, my brother's .284 winchester and the Berger 180s).

I apologize to everyone and do not want to hijack the thread, which deals with much bigger projectiles then mentioned here.

JeffVN

 

[Emouse]

Re: Promised S. ELR Bullet CFD

Nice work indeed guys,...is the CFD software geared toward being a publically accessable variant of what PRODAS can do??

GROPER, I think posted the bullet schematic to show what a varaiant of the LM thought process would and could look like. The LM bullets do need specific twist rates to optimise them, out of the norm, again as noted by Bryan.

 

[Emouse]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: groper</div><div class="ubbcode-body">No, bands generally do not cause more fouling...

My designs do not call for super fast barrel twist rates, which is one of the more appealing aspects of my conceptual designs... most people will be able to use a super high BC bullet from their existing barrel they shoot jacketed bullets from. My main focus has always been on stability as everything else follows from there. If you have more stability to work with, you can make a bullet longer, heavier and therefore more BC potential, from any given twist rate barrel... make sense? I currently have design models for 338cal in 1:9-10twists, 375cal in 1:9-10 and special one for 1:8twists, presently working on 30cal 1:10twist. All versions in both hollow point and solid. I dont really see any point in working on any caliber less than 30cal at this point, as they will be too expensive for that market to tolerate. The machining involved in these designs has many more steps and soaks up alot more machine time than a typical banded VLD projectile. ill look into it if the interest is there however...



</div></div>

Yes,..exactly right.

 

[Noel Carlson]

Re: Promised S. ELR Bullet CFD

Bohem,

It is good to see a serious turn to the discourse on 6+ caliber projectiles, but judging from view counts... this is going to draw much less interest. It is just as well in my opinion.

Your comment on apparent BC drop at 338 caliber has another dimension than simple manufacturing inertia. There actually is a precipitious drop in the stabilizing effect, of compensating tail design, that occurrs somewhere between 30, and 338, caliber that would be worth a closer look through cfd analysis.

Btw, the modeled projectile will not stabilize in anything larger than a fourteen caliber exit-twist, and the muzzle velocity would have to stay at, or below approximately Mach 2. If the same projectile sported one of the trendy "rounded" tails, performance would be further compromised.

Emouse,

Well, almost exactly. Refinement of the projectile form permits use of lower density material, and "lighter" weight... all other considerations being equal.

 

[bohem]

Re: Promised S. ELR Bullet CFD

Hi Noel-

Glad to see you found the thread, I'd like to discuss your thoughts on the CFD idea in general. I'll send you a PM and maybe we can setup a time to talk.

 

[frankythefly]

Re: Promised S. ELR Bullet CFD

bohem what program where you using for your first post above? Is that Autodesk Inventor?

 

[bohem]

Re: Promised S. ELR Bullet CFD

I don't know what Groper used to model the bullet in for CAD, the CFD is a proprietary solution that Ply1951Guy wrote and he has a pre/post processing program for it that is an off the shelf solution.

 

[groper]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Noel Carlson</div><div class="ubbcode-body">Bohem,

If the same projectile sported one of the trendy "rounded" tails, performance would be further compromised.
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I had a good chuckle at that, nice one Noel...

 

[steve123]

Re: Promised S. ELR Bullet CFD

Coming from the non biased end of things.

I wonder which one of the "smart bullet maker dudes" is going to win the "solid projectile wars"??? I sure hope somebody does so soon because it's been years,it seems,and I'm going to be ready for a new barrel soon for my 375CT.

 

[Augustus]

Re: Promised S. ELR Bullet CFD

There wil not be a clear winner. There will be several variations using slightly different approaches requiring slightly different twists. The winner will be deciced by who is the best businessman. Whoever can deliver the product the fastest and cheapest while maintaining tight tolerences will win the war.

 

[groper]

Re: Promised S. ELR Bullet CFD

2011 is gonna be a great year, the projectiles everyone is working on offer something slightly different, whether it be confined by twist rate, outright top BC, or special barrels etc... the only clear winners will be ELR shooters in general.

Merry xmas everyone, look forward to the new year.

 

[Noel Carlson]

Re: Promised S. ELR Bullet CFD

Groper,

Very well said.

 

[steve123]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: groper</div><div class="ubbcode-body">2011 is gonna be a great year, the projectiles everyone is working on offer something slightly different, whether it be confined by twist rate, outright top BC, or special barrels etc... the only clear winners will be ELR shooters in general.

Merry xmas everyone, look forward to the new year. </div></div>

Yes,Merry Christmas too all!!!

 

[Gerard Schultz]

Re: Promised S. ELR Bullet CFD

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Btw, the modeled projectile will not stabilize in anything larger than a fourteen caliber exit-twist, and the muzzle velocity would have to stay at, or below approximately Mach 2.</div></div>Twist 1:8" in a .57"caliber, max speed 2200fps and a BC of 1.2
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If the same projectile sported one of the trendy "rounded" tails, performance would be further compromised.</div></div>Yes, that did raise a smile.

A belated blessed Christmas and a prosperous new year to all.