Hyper Stabilized Bullets - Jim Boatright

Lowlight

HMFIC of this Shit
Staff member
Apr 12, 2001
27,017
2,536
113
Base of the Rockies
www.snipershide.com
I actually saw a video at SHOT with fluid testing and air flow in a way I had not seen before

it can give you lateral information too,

In fact, in the same place, the owner of the video has a nanotechnology that completely changes the rules on a bullet works. His coatings would allow a bullet to "FLY" underwater.
 
Likes: Bender

THEIS

Sergeant of the Hide
Nov 27, 2017
949
1,412
93
Hi,

LL is that coating company up and running in regards to coating bullets commercially yet or they still in T&E phase?

Sincerely,
Theis
 

Lowlight

HMFIC of this Shit
Staff member
Apr 12, 2001
27,017
2,536
113
Base of the Rockies
www.snipershide.com
It's running, but I believe they are still confirming the process properly coats the bullets. it's actually a very cheap and easy process. They sort of just drop the bullet in a solution and when it hits the bottom it is done.

But the tech is there, and I have seen the simulations they use to test.
 
Likes: Bender

THEIS

Sergeant of the Hide
Nov 27, 2017
949
1,412
93
Hi,

My new Schneider P5 7 twist .375 ships Wednesday.
Looking forward to testing the MkII projectiles very soon. If initial testing goes well we will book the RUAG testing facility in Thun for further testing.

Sincerely,
Theis
 
Likes: CPierce

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
Hi,

FSG...I am not sure if this link is the exact same document as the previous link but here you go.

https://arxiv.org/ftp/arxiv/papers/1205/1205.2071.pdf

Sincerely,
Theis
As of today, that 2012 paper has been updated on arXive and Research Gate websites. The arXive reference number is still the same: 1205.2071. That is in their classical physics section. The title is still "A Coning Theory of Bullet Motions." I sent a PDF of it to Gustavo and asked him to send it to Frank.
Jim Boatright
 

CPierce

New Hide Member
Feb 22, 2018
2
0
1
As of today, that 2012 paper has been updated on arXive and Research Gate websites. The arXive reference number is still the same: 1205.2071. That is in their classical physics section. The title is still "A Coning Theory of Bullet Motions." I sent a PDF of it to Gustavo and asked him to send it to Frank.
Jim Boatright
Jim, you should probably put it in the "Resource Section" here as well
 

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
UPDATE:
The accuracy problem experienced in short-range testing of my drilled-base 338 copper ULD bullets turned out to be a muzzle brake problem which I had caused in align-boring it. I got the holes through the baffles too large which allows gas bypass at speeds high enough to destabilize the bullet bases due to differential gas pressures. The new 7-twist Schneider barrel works very well initially. It has no MB at present. There was never a problem of powder packing into the bullet bases with VV N560, Alliant RL-25, or RL-26. I will report what kind of short-range accuracy we can get with these 338 bullets--so far, it looks like well under 0.25-inch for 5-shot extreme spread.

I see no reason that we cannot have excellent short-range accuracy with ELR/ULR bullets and loads. Short-range accuracy is a necessary, but not sufficient, condition for ELR accuracy. If we add a requirement for better uniformity of bullet speed out of the muzzle, that short-range accuracy implies long-range accuracy capability. Measuring the horizontal crosswind accurately just in front of the muzzle allows correcting elevation aim-point for CWAJ at all ranges. Even as the hyper-stable bullet damps out that initial coning angle-of-attack (W/V) within the first 40-yards of flight, that CWAJ aiming correction is still needed.
 
Last edited:
Likes: TiroFijo

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
David test-fired the solid (non-drilled) 242-gr version of my original ULD bullet today. He got quite similar results as in his first test-firing of the 225-gr drilled bullets. The outside dimensions of the two bullets are identical. His Oehler System 88 calculated a 5-shot average BC(G1) of 0.835 with an average airspeed of Mach 2.44 for these heavier bullets over 997 yards. McDRAG calculated a BC(G1) of 0.7507 for this airspeed. This time the measured BC is 11.2 percent larger than the McDRAG estimate instead of 12.9 percent larger. Once again, the 5 individual shot measurements were quite consistent among themselves. These 242-gr bullets have an Iy/Ix ratio of 13.5 versus 12.0 for the base-drilled version (largely why we drilled them). So, the initial Sg was only 2.45 instead of 2.75 from David's 7.5-inch twist Schneider barrel at 3335 fps average MV. I recommended that he get Gary to make him a 6.5-inch twist 338-caliber barrel.
 

FlaShooterG

New Hide Member
Jan 21, 2018
73
11
8
Jim,
For purposes of ELR, would solid bullets be of benefit for say 6.5 rounds? I am guessing they would be heavier and perhaps more stable???
 

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
Jim,
For purposes of ELR, would solid bullets be of benefit for say 6.5 rounds? I am guessing they would be heavier and perhaps more stable???
The base-drilled copper 6.5 mm ULD bullets are currently being prototyped by Dan Warner. They weigh 105 grains and should be fireable from barrels having an 8-inch twist-rate. In warm weather, they should work from my 8.5-inch twist Krieger barrels. Depending on muzzle speed, they should stay supersonic farther than 1500 yards with an estimated BC(G1) of 0.597 at Mach 2.5, or a BC(G7) of 0.299 in any speed range, about like a good 140-gr jacketed bullet, but fired much faster.

The Mark II 6.5 ELR bullet will weigh only 118.3 grains. It has an extended 3.2-caliber secant ogive, but no base drilling. It would have an initial gyroscopic stability of 3.17 when fired from a 5-inch twist barrel for hyper-stable flight. It should be a really good ELR bullet, with an estimated BC(G1) of 0.690 at Mach 2.5. The BC(G7) should be about 0.342 in any speed range. All of these BC estimates are for hyper-stable flight.
 
Last edited:

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
Jim,
Any updates on testing info of the larger ELR bullets?
Not much progress to report right now, MP. Dan Warner has made some solid 6.5 mm bullets, but we don't have a fast-twist barrel to really fire them from. We are awaiting a testable quantity of base-drilled 6.5 mm 105-gr bullets and a 7-inch twist 6.5 barrel for firing both these 105-gr ULD bullets and 140-gr class lead-core bullets.. Next will be the 254-gr Mk II 338-caliber ELR bullets. Then will be the 346-gr Mk II 375-caliber ELR bullets.
 
Likes: Milepost
Dec 30, 2017
25
6
3
Pacific Northwet
I am ordering up a 28" 7 twist barrel this week for a 6.5 saum. The 346-gr Mk II ELR sounds really interesting, especially if it is shot from a 416 Barrett case! Only problem I see might be finding a slow powder for such a large overbore...
 

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
I am ordering up a 28" 7 twist barrel this week for a 6.5 saum. The 346-gr Mk II ELR sounds really interesting, especially if it is shot from a 416 Barrett case! Only problem I see might be finding a slow powder for such a large overbore...
We also have at 28-inch, 7-twist, 6.5 mm barrel on order (dual-purpose 6.5/284 for 140-gr class lead-core bullets and 105-gr copper bullets). Our 7-twist 338 Schneider P5 barrel will be ready soon, properly fitted with a Light, Air-Working (LAW) muzzle brake by Mic McPherson of Cortez CO . It is a "match" 338 Lapua Magnum chambering. Theis is planning to test the 375-ELR bullets at 4000 fps from his 7-twist Schneider barrel. Said something about a necked-down BMG cartridge. Those 375's might remain supersonic to almost 4000 yards at Whittington (if the place hasn't burned up).
 
Last edited:
Likes: Milepost

THEIS

Sergeant of the Hide
Nov 27, 2017
949
1,412
93
Hi,

I finally got the correct shoulder angle reamer in hand!! We are finishing up our new BMG class receiver next week. I am going to meet with Roy Couvillion (Guy that helped Dr. Courtney with suppressor article) the week after next to discuss his suppressor design in regards to the big boomers.

Sincerely,
Theis
 
Likes: Milepost

Old Dude

New Hide Member
May 12, 2018
25
10
3
Would there be any differences between 6, 5,or 3 groove rifling in the initial yaw of the bullet leaving the barrel? I am asking because my thinking tells me that a larger volume 3 groove gas pathway could have larger tolerance cross sectional areas. Whereby the volume of gas in each pathway could impart a differing velocity or pressure on the bullet base as it exits the bore. Thereby increasing the bullets initial instability. I'm a noob with a high performance engine building background and this conversation is way over my math skills but it's a blast to read.
 

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
Would there be any differences between 6, 5,or 3 groove rifling in the initial yaw of the bullet leaving the barrel? I am asking because my thinking tells me that a larger volume 3 groove gas pathway could have larger tolerance cross sectional areas. Whereby the volume of gas in each pathway could impart a differing velocity or pressure on the bullet base as it exits the bore. Thereby increasing the bullets initial instability. I'm a noob with a high performance engine building background and this conversation is way over my math skills but it's a blast to read.
I have not looked in depth into rifle bullet destabilization during transit of the muzzle blast region. Perhaps others might have done so. That being said, by radically increasing the axial rigidity of the hyper-stabilized spinning bullet, any destabilization of the fired bullet should be minimized in the blast zone. The number and type of rifling grooves selected is probably of lesser importance for marginally stabilized bullets than the design of the bullet's base. A proper boat-tail designed for optimum nose-forward flight might not be optimum during the 5 milliseconds, or so, transit time in the blast zone. In particular my bullet's sharp, non-radiused, rear corners and flat or concave base are probably more destabilizing than the usual rounded over corners and convex base of jacketed bullet bases. Fired rifle bullets must start out by briefly "flying backwards" right out of the muzzle.

So, no, I do not see the choice of rifling pattern affecting bullet destabilization for any hyper-stabilized rifle bullet. I do favor rifling patterns which grip the bullet shank (or driving band(s), adequately for proper spin-up of the projectile and seal (obturate) the bore well so as to prevent gas leakage past the engraved bullet in the bore. Having rounded (radiused) inside corners at each side of every groove is a key rifling design feature. I particularly like Gary Schneider's P5 rifling for its obturation qualities. Poor obturation is a more serious rifle problem than most realize, especially in firing non-deforming copper bullets.
 
Likes: Old Dude
Dec 30, 2017
25
6
3
Pacific Northwet
I would think that the design of the the muzzle brake gas pathway would have a larger impact on the initial accuracy. But, I've heard that all boattail bullets have some wobble as they leave the barrel and then will stabilize within the first couple hundred yards. Some 50 BMG bench rest shooters will use 300 yards to check for accuracy instead of 100 because of this.
 

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
Yes, those 50-caliber barrels should have been made with a 10-inch per turn twist-rate. The standard 15-inch twist was always marginal for gyroscopic stability.
 
Dec 30, 2017
25
6
3
Pacific Northwet
Jim,

Does the radiused rifle grove also decrease some of aerodynamic drag imparted by conventional rifling to the laminar air flow as the bullet spins thru the air? If so, wouldn't a swedged hammer forged design rifling similar to what H & K uses be best?

I guess one could take it one step further and then use this for a modern "SLAP" style design.....
 
Last edited:

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
No, MP, the boundary layer airflow should be laminar only over the ogive of properly designed rifle bullet. The flow over the bullet shank and afterbody should be turbulent. In any case, the 3 to 5 thou depth of the rifling engraving is completely submerged within the boundary layer and cannot affect the aeroballistics of bullet flight. That is why we do not need to polish our rifle bullets, for example.
 
Likes: TiroFijo

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
Yes, those 50-caliber barrels should have been made with a 10-inch per turn twist-rate. The standard 15-inch twist was always marginal for gyroscopic stability.
The part of my reply to MP got lost where I referred him to the discussion of the "VLD accuracy problem" in my paper on Third Generation Rifle Bullet design posted here in the Resources section. That is a discussion of the in-bore yaw problem with boat-tailed secant-ogive VLD bullets.
 
Likes: Milepost

THEIS

Sergeant of the Hide
Nov 27, 2017
949
1,412
93
THEIS,

I see that you are running a Schneider barrel. What is the length will you be using? Would you happen to know the max length they can machine?

Thanks
Hi MP:
I am not sure what their max length is. I will contact Gary and see. I know for the 1 I have right now the length is not over 32" but that was because my .375 barrel is made from the alloy and lengths he uses for the BMG barrels since it is going in a new BMG class receiver and not the standard CT class receivers and I did not want to wait for something longer lol.


Yes, those 50-caliber barrels should have been made with a 10-inch per turn twist-rate. The standard 15-inch twist was always marginal for gyroscopic stability.
Hi Jim,
That will have to be my next acquisition...now just have to get Gary to make new tooling :)

Sincerely,
Theis
 
Last edited:
Dec 30, 2017
25
6
3
Pacific Northwet
Thanks Jim, that makes total sense..especially considering super-sonic flight dynamics. But what about subsonic? I do realize the point of your design is to extend the range and accuracy by keeping the bullet above Mach well past two miles for ELR.

Most competitors in the KO2M are shooting conventional slower twist designs and are subsonic for hundreds of yards before 2 miles. In this case, does the rifling still remain submerged in the boundary layer during subsonic flight? Isn't there a lot of yaw induced into the bullet during the last portion of the trajectory for ELR that could effect the boundary layer airflow?

BTW - I saw a funny YT video of a guy shooting a 50 BMG straight up. As the bullet came back down you could hear the whirling sounds caused by the rifling. Yes, I know the bullet was probably only traveling just a few hundred FPS and it was surplus Junk ammo but it does make you think... If you can hear it than it must be disturbing the air.

PS Sorry, I didn't mean to derail your thread, just a little curious about the subsonic ballistics of bullet design tool
I'll will read your paper that is located in the resource section....Thanks again
 
Last edited:

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
Thanks Jim, that makes total sense..especially considering super-sonic flight dynamics. But what about subsonic? I do realize the point of your design is to extend the range and accuracy by keeping the bullet above Mach well past two miles for ELR.

Most competitors in the KO2M are shooting conventional slower twist designs and are subsonic for hundreds of yards before 2 miles. In this case, does the rifling still remain submerged in the boundary layer during subsonic flight? Isn't there a lot of yaw induced into the bullet during the last portion of the trajectory for ELR that could effect the boundary layer airflow?

BTW - I saw a funny YT video of a guy shooting a 50 BMG straight up. As the bullet came back down you could hear the whirling sounds caused by the rifling. Yes, I know the bullet was probably only traveling just a few hundred FPS and it was surplus Junk ammo but it does make you think... If you can hear it than it must be disturbing the air.
Subsonic flight is sirene and can be extremely low drag (Cd = 0.003 is possible). It is in the several hundred yards of chaotic transonic flight where problems arise. The boundary layer acts about the same throughout the bullet's flight. We do not fully understand what happens with different projectiles in the transonic region. Good subsonic bullets seem also to work better in transonic flight. Unfortunately, the bullet design drivers are sort of opposite from those of optimum supersonic projectiles. A good low-speed projectile should be heavy, short, fat, and have about a 2-caliber elliptical nose. Think of a 500-gr 45-caliber lead slug with that elliptical nose. I do not like any type of "spire point" or central tit on a subsonic bullet. It interferes with the free movement of the aerodynamic stagnation point. The subsonic boat-tail should probably be somewhat longer and shallower-angled also. A properly designed rebated boat-tail can also work well in subsonic flight. I do believe that hyper-stability will also prove beneficial in transonic and subsonic flight.

The whirring noise of subsonic bullets is due to their coning motion, nothing to do with rifling marks. I hope everyone around that fool was wearing a helmet and not looking upward.

Jim Boatright
 
Feb 20, 2013
451
25
28
Everybody says that a bullet needs to cover certain amount of ground before Sg takes place. For a common rifle bullet, how much yardage is really needed? Tenths? Hundreds?
 

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
Everybody says that a bullet needs to cover certain amount of ground before Sg takes place. For a common rifle bullet, how much yardage is really needed? Tenths? Hundreds?
First, aeroballistic flight does not begin until the bullet penetrates the muzzle blast shockwave, usually about 3 to 6 yards in front of the rifle barrel's muzzle.

Gyroscopic stability (Sg) is a measure of the spin-stabilized rifle bullet's ability to withstand the aerodynamic overturning moment in atmospheric aeroballistic flight. It really has no meaning in the muzzle blast flight regime. Sg can be calculated as P squared over 4M, where P is related to the axial rigidity of the spin-stabilized bullet and M is related to its instantaneous aerodynamic overturning moment.

All else being equal, the aerodynamic overturning moment varies linearly with atmospheric density (rho). In flat firing the air density remains essentially constant throughout the flight. As the rifle bullet slows in flight, its overturning moment decreases with the square of its velocity through the air. Since the spin-rate of the bullet slows only exponentially with time of flight (very gradually), Sg always increases throughout the supersonic flight of any rifle bullet in flat firing.

I suspect that your question relates to when in the flight the initial coning motion of the typical rifle bullet damps down enough to allow minimum-coning-angle-of-attack (hyper-stable) ballistic flight. It is sometime said that the bullet has "gone to sleep" when its air drag has decreased to its minimum nose-forward value (CD0). The aeroballistic damping factor (lambda-2) which determines this point is related to the dynamic stability (Sd) of the rifle bullet. With a 20 calibers per turn rifling twist, this can occur in the first 10 to 20 yards of aeroballistic flight. For slow-twist conventional barrels, this typically requires 200 to 600 yards of higher yaw-drag flight. With an initial Sg of about 1.8, it might only require 200 yards, but with an initial Sg as low as 1.2, it might require more like 600 yards of flight distance before the initial coning angle is really damped out.

I hope this answers your question.

Jim Boatright
 
Likes: LastShot300

lash

Swamp Rat
Sep 28, 2012
3,185
869
113
59
Central Florida
First, aeroballistic flight does not begin until the bullet penetrates the muzzle blast shockwave, usually about 3 to 6 yards in front of the rifle barrel's muzzle.

Gyroscopic stability (Sg) is a measure of the spin-stabilized rifle bullet's ability to withstand the aerodynamic overturning moment in atmospheric aeroballistic flight. It really has no meaning in the muzzle blast flight regime. Sg can be calculated as P squared over 4M, where P is related to the axial rigidity of the spin-stabilized bullet and M is related to its instantaneous aerodynamic overturning moment.

All else being equal, the aerodynamic overturning moment varies linearly with atmospheric density (rho). In flat firing the air density remains essentially constant throughout the flight. As the rifle bullet slows in flight, its overturning moment decreases with the square of its velocity through the air. Since the spin-rate of the bullet slows only exponentially with time of flight (very gradually), Sg always increases throughout the supersonic flight of any rifle bullet in flat firing.

I suspect that your question relates to when in the flight the initial coning motion of the typical rifle bullet damps down enough to allow minimum-coning-angle-of-attack (hyper-stable) ballistic flight. It is sometime said that the bullet has "gone to sleep" when its air drag has decreased to its minimum nose-forward value (CD0). The aeroballistic damping factor (lambda-2) which determines this point is related to the dynamic stability (Sd) of the rifle bullet. With a 20 calibers per turn rifling twist, this can occur in the first 10 to 20 yards of aeroballistic flight. For slow-twist conventional barrels, this typically requires 200 to 600 yards of higher yaw-drag flight. With an initial Sg of about 1.8, it might only require 200 yards, but with an initial Sg as low as 1.2, it might require more like 600 yards of flight distance before the initial coning angle is really damped out.

I hope this answers your question.

Jim Boatright
It may not have answered his question, but it sure did help to fill in a further understanding of what happens with some projectiles, for me. Like the .338 255.6 g Flatlines out of a marginally twisted 1:9 (according to new theory on flight/coning stability). They do not group well for me at shorter distances. That is, they do not group terribly, but certainly not as well as the 285 g Hornadys do at 100-1000 yards. Yet, once at 1500-2000 yards, these settle in really well and have made me proud a time or so. I am left wondering how well they will perform in an 8.25-6.75 left hand gain twist barrel. That is a future project I could get behind. Current projects currently overshadow it right now.
 
Likes: LastShot300

THEIS

Sergeant of the Hide
Nov 27, 2017
949
1,412
93
Hi,

A cheap experiment aka test is finding a range with pits (That you can get farther from the targets than the "square" range area) and listen to projectiles at various velocities go over the protection of the pits.

The sound is very distinguishable from supersonic to full blown subsonic. Hearing a 300gr .338 SMK that was fired from 2000m away is very different than sound when it was fired from 3000m away. The sound you hear when it passes over the pits from 3000m away is like listening to someone blow one of those hand held pinwheels. You can just hear that projectile beating the air up.

Sincerely,
Theis
 
Feb 20, 2013
451
25
28
First, aeroballistic flight does not begin until the bullet penetrates the muzzle blast shockwave, usually about 3 to 6 yards in front of the rifle barrel's muzzle.

Gyroscopic stability (Sg) is a measure of the spin-stabilized rifle bullet's ability to withstand the aerodynamic overturning moment in atmospheric aeroballistic flight. It really has no meaning in the muzzle blast flight regime. Sg can be calculated as P squared over 4M, where P is related to the axial rigidity of the spin-stabilized bullet and M is related to its instantaneous aerodynamic overturning moment.

All else being equal, the aerodynamic overturning moment varies linearly with atmospheric density (rho). In flat firing the air density remains essentially constant throughout the flight. As the rifle bullet slows in flight, its overturning moment decreases with the square of its velocity through the air. Since the spin-rate of the bullet slows only exponentially with time of flight (very gradually), Sg always increases throughout the supersonic flight of any rifle bullet in flat firing.

I suspect that your question relates to when in the flight the initial coning motion of the typical rifle bullet damps down enough to allow minimum-coning-angle-of-attack (hyper-stable) ballistic flight. It is sometime said that the bullet has "gone to sleep" when its air drag has decreased to its minimum nose-forward value (CD0). The aeroballistic damping factor (lambda-2) which determines this point is related to the dynamic stability (Sd) of the rifle bullet. With a 20 calibers per turn rifling twist, this can occur in the first 10 to 20 yards of aeroballistic flight. For slow-twist conventional barrels, this typically requires 200 to 600 yards of higher yaw-drag flight. With an initial Sg of about 1.8, it might only require 200 yards, but with an initial Sg as low as 1.2, it might require more like 600 yards of flight distance before the initial coning angle is really damped out.

I hope this answers your question.

Jim Boatright
Jim, thanks a lot for your thorough reply(y)
 
Feb 20, 2013
451
25
28
It may not have answered his question, but it sure did help to fill in a further understanding of what happens with some projectiles, for me. Like the .338 255.6 g Flatlines out of a marginally twisted 1:9 (according to new theory on flight/coning stability). They do not group well for me at shorter distances. That is, they do not group terribly, but certainly not as well as the 285 g Hornadys do at 100-1000 yards. Yet, once at 1500-2000 yards, these settle in really well and have made me proud a time or so. I am left wondering how well they will perform in an 8.25-6.75 left hand gain twist barrel. That is a future project I could get behind. Current projects currently overshadow it right now.
Have a friend with the same gripes! Follow up will be greatly appreciated.
 

TripleBull

This one goes to 11
Feb 13, 2017
2,362
4,275
113
Sunny Colorado
Hi,

A cheap experiment aka test is finding a range with pits (That you can get farther from the targets than the "square" range area) and listen to projectiles at various velocities go over the protection of the pits.

The sound is very distinguishable from supersonic to full blown subsonic. Hearing a 300gr .338 SMK that was fired from 2000m away is very different than sound when it was fired from 3000m away. The sound you hear when it passes over the pits from 3000m away is like listening to someone blow one of those hand held pinwheels. You can just hear that projectile beating the air up.

Sincerely,
Theis
I've done this at 200 yard increments from super to sub. I have a good portable recording rig and mics and plan to make some quality stereo recordings of the differences.
 

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
The 50-caliber M2 bullet weighs only 650 grains, IIRC. It is very "short" and "fat" by ballistic standards, which allows its use in 15-inch twist-rates. Scaled to 30-caliber, it would weigh only 140.4 grains. A ballistically "proper" lead-cored 50-caliber bullet would weigh about 900+ grains. That would be a scaled-up 200-gr 30-caliber match bullet. My recommended 10-inch twist-rate is 20-calibers per turn for 0.5-inch bullets.
 
Likes: THEIS

Skookum

Flattus Domini
May 6, 2017
691
572
93
Your mom's
I zero my AR-50 at 500 yards. Anything shorter than that is just pointless if you want to shoot "long".
This means nothing without more detail. Are you telling us that you use such a canted base, that you can't zero any closer than 500 yards? Or, are you saying that you just zero at 500 and hold for elevation changes? Or, do you just arbitrarily zero at 500 yards? I would love to hear your reasoning for the last two.
 
Dec 30, 2017
25
6
3
Pacific Northwet
I zero my AR-50 at 500 yards. Anything shorter than that is just pointless if you want to shoot "long".
So let's look at a 750 gr. A-max @2800 fps from the barrel at sea level. It hits the sonic barrier at 2050 yards. At that range you need 79.35 MOA with a 100 yard zero. With a 500 yard zero you need 71 MOA. Just little bit over 8 MOA more... WOW!!...I think I can handle that .

.50 is just a scaled up .30-06 and that "standard" twist rate is from M2 machine guns. It works just fine for the cartridge.
Duh....Machine guns don't have to be very accurate. A 15 twist works fine for A/P & tracer ammo. The top match shooters have been using 750 - 800 gr. mono bullets with a 13 twist and single feed actions. In the lightweight ( under 32.5 lb. ) tactical class they will use the lighter/shorter mono bullets using a Steyr, Barrett, AI etc... The smaller lighter mag length bullets can still get away with the slower 15 twist but a faster twist would still always be better.

BTW- Years ago I thought that a 11 or 10 twist barrel is all you needed on a .308. Now the USMC M40A6 uses a 8 twist. Time marches on. The new bullet designs, powders, better barrels and new revelations of interior/ exterior ballistics can still teach an old dog new tricks.

Time will tell if Jim's hyper stabilized theory is true. There is some really good sound science behind it. I'm betting he's right because I just ordered a 36" 8 twist barrel coming for my 416 improved.
 
Last edited:
Likes: lash

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
I am glad to hear of your vote of confidence in hyper-stability, MP. By moving to a 50-percent faster barrel twist rate, you will be exploring new, uncharted territory. You will have resolved several old problems, but who can say when new problems might arise. I do not foresee any, but time and experience will tell. Once you try hyper-stabilizing your fired bullets, I don't think you will ever wish to go back, at least for ELR shooting.

I have not been upset in any way by the disparaging off-topic remarks of CHS. They are not substantive criticisms. As a "ballistician" and "scientist," I agree that I do not find ballistic coefficient (BC) to be a particularly useful concept, preferring actual coefficients of aerodynamic drag (Cd) as functions of Mach speed. I also have the utmost respect for John Moses Browning and his creations. My EDC pistols are 1911's, which I made. I think Browning would have approved of Jim Clark's 460 Rowland conversion. I also wrote a letter to my US Senator in 1995 requesting that Carlos Hathcock be awarded the Medal of Honor for his actions in saving the lives of several Marines after his transport vehicle was blown up by an IED in Viet Nam. Unfortunately, that scumbag, Bill Clinton, did not agree.
 
Likes: LastShot300
Dec 30, 2017
25
6
3
Pacific Northwet
Jim
Would a mild gain twist be of any advantage ( 11 to 10 ) or would you suggest going with a straight 10 for a 50BMG. I will be going with a 36" Bartlein barrel. Schneider can't go any longer than a 32" and it would be conventional rifling.

BTW ... When I talked to Bartlein they said that they would modify their 5R rifling to suit the 50 BMG fast twist. Thereby tweaking the groove width and using different angles of cant unique to each side. Should make for less fowling and supposedly a faster barrel too!
 

Jim Boatright

New Hide Member
Feb 21, 2018
75
60
18
I see no reason to bother with a gain-twist barrel, especially for larger calibers. All modern rifle cartridges operate at about 60,000 psi, more or less, as a peak chamber pressure. The peak base-pressure on the bullet is usually about 90-percent of the peak chamber pressure. The peak force accelerating the bullet is the peak base-pressure times the cross-sectional area of the bore, which in turn varies with the square of the caliber. The acceleration of the bullet in the barrel is essentially the driving force divided by the mass of that bullet (neglecting barrel friction and other losses). The mass of a given bullet design varies with the cube of its caliber. So, the peak forward acceleration decreases with caliber (ie, varies inversely with the first power of its caliber dimension). With constant twist-rate barrels, the peak spin-up rate required of the bullet is therefore proportional to peak chamber pressure and inversely proportional to caliber. If rifling with a 9-degree helix angle (20 calibers per turn) works well with a small-caliber bullet of a given design and construction, it will certainly work for larger-caliber examples of that same bullet.

As a point of interest, after examining several recovered copper 338-caliber and 6.5 mm bullets of my new design fired at about 3000 fps into a swimming pool, I note that the 6.5 mm bullets expanded elastically during firing while the 338-caliber bullets of the same design and construction did not expand nearly as much in the bore. Peak acceleration of the 6.5 bullets was about 200,000 g's, but it was only a little over 100,000 g's for the 338's. There was no permanent (plastic) in-bore distortion of any recovered bullets. The prototype 6.5 mm bullets were actually made 0.0002-inch under diameter, but the elastic diametral expansion during firing managed to align the bullets accurately in the bore and to seal the powder gasses reasonably well.
 
Last edited:
Feb 7, 2013
2,103
527
113
The West
I see no reason to bother with a gain-twist barrel, especially for larger calibers. All modern rifle cartridges operate at about 60,000 psi, more or less, as a peak chamber pressure. The peak base-pressure on the bullet is usually about 90-percent of the peak chamber pressure. The peak force accelerating the bullet is the peak base-pressure times the cross-sectional area of the bore, which in turn varies with the square of the caliber. The acceleration of the bullet in the barrel is essentially the driving force divided by the mass of that bullet (neglecting barrel friction and other losses). The mass of a given bullet design varies with the cube of its caliber. So, the peak forward acceleration decreases with caliber (ie, varies inversely with the first power of its caliber dimension). With constant twist-rate barrels, the peak spin-up rate required of the bullet is therefore proportional to peak chamber pressure and inversely proportional to caliber. If rifling with a 9-degree helix angle (20 calibers per turn) works well with a small-caliber bullet of a given design and construction, it will certainly work for larger-caliber examples of that same bullet.

As a point of interest, after examining several recovered copper 338-caliber and 6.5 mm bullets of my new design fired at about 3000 fps into a swimming pool, I note that the 6.5 mm bullets expanded elastically during firing while the 338-caliber bullets of the same design and construction did not expand nearly as much in the bore. Peak acceleration of the 6.5 bullets was about 200,000 g's, but it was only a little over 100,000 g's for the 338's. There was no permanent (plastic) in-bore distortion of any recovered bullets. The prototype 6.5 mm bullets were actually made 0.0002-inch under diameter, but the elastic diametral expansion during firing managed to align the bullets accurately in the bore and to seal the powder gasses reasonably well.
Jim,

The only thing this dumb ass understood, is... I am not swimming in your pool!!



Honestly, thanks for all the time and your posts..

Jt
 
Likes: LastShot300

mijp5

Gunny Sergeant
May 7, 2009
4,571
1,655
113
Jim, or anyone else who can answer this question:

At what point does a twist effectively fail to turn a bullet progressing forward thru the barrel? In other words, won’t at some point the twist rate get too tight that the projectile will actually skip over the rifling? The fastest twist I know of is a 5 twist in my 300 blk. How much tighter can you go?
 

Skookum

Flattus Domini
May 6, 2017
691
572
93
Your mom's
Jim, or anyone else who can answer this question:

At what point does a twist effectively fail to turn a bullet progressing forward thru the barrel? In other words, won’t at some point the twist rate get too tight that the projectile will actually skip over the rifling? The fastest twist I know of is a 5 twist in my 300 blk. How much tighter can you go?
A barrel maker close to me, told me personally that he is making some 1/3 twist 50 cal barrels for some entity to test. PO Ackley, in one of his books, mentioned testing twists as tight as 1/1.
 

Skookum

Flattus Domini
May 6, 2017
691
572
93
Your mom's
Jim, I would be interested to know of any trends or abnormalities you have noticed with reloading these tight twist rounds. How has it affected powder burn rates, powder choices, accuracy nodes, velocities, etc.
 
Feb 7, 2013
2,103
527
113
The West
You guys are only thinking solids, correct? I lost a chrono (before Labradars and MS) spinning a traditional to fast. Just asking for clarification.
 
Last edited:
Top Bottom