Why not take this a step further and do testing with viscous liquid/material injected into the core of a bullet as to serve as a instability buffer.
Maybe some of Frank's leftover Spin D?
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Why not take this a step further and do testing with viscous liquid/material injected into the core of a bullet as to serve as a instability buffer.
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
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,
Any updates on testing info of the larger ELR bullets?
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...
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.
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.
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 Jim,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.
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.
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?
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.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 replyFirst, 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
Have a friend with the same gripes! Follow up will be greatly appreciated.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.
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
That would be cool to hear.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.
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.I zero my AR-50 at 500 yards. Anything shorter than that is just pointless if you want to shoot "long".
Fuck me running, I think this forums average IQ dropped about 30 points with the arrival of this new member.
I zero my AR-50 at 500 yards. Anything shorter than that is just pointless if you want to shoot "long".
.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.
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.
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.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?