Progress in Developing Copper ULD Bullets

[Jim Boatright]

Jim is this muzzle device of your design?

While I was mentally imagining this design, I saw the MB attached to the barrel of the prototype Winchester Automatic Rifle (WAR) in the Cody Firearms Museum collection. That rifle was successfully demonstrated to the Army in December of 1944, but dropped completely after VJ-Day. The exit nozzle is my only real modification to Winchester's work. The screenshots are from Ian McCollum's Forgotten Weapons video on the WAR from a few years ago.

 

[Jim Boatright]

Jim is this muzzle device of your design?

No, JB.IC, this particular muzzle brake might have been designed in 1944 by somebody at Winchester, but does not seem to have been patented. While mentally designing one quite similar, I ran across this one example on the "EXP" marked Winchester Automatic Rifle in 30-'06 from the collection at the Cody Firearms Museum. It is pictured in Bruce Canfield's new book "The US Small Arms of WWII." I added the exhaust nozzle as my own requirement to minimize yaw destabilization of the fired bullets.

If any records of the origination of this MB design ever existed, they seem to have been disposed of during the great demobilization after VJ-Day. Bruce Canfield is looking in Edwin Pugsley's papers for any information on this. I would like to credit the inventor of this unique MB.

EDIT: I thought my earlier reply had been lost when it did not appear after refreshing the screen. Hence the double reply. I see what happened now. I did not see the 2nd (Next) page symbol below the "Write your reply..." box where I looked for it. It is above it instead.

 

[timintx]

'You are correct, Max, that the harmonic standing wave transverse vibrations of a center-fire rifle barrel occur after the bullet has departed"


Jim you are my ballistic hero but I have have to say these waves can be slowed up or sped up to see , with that said I
have been able to manipulate vertical bending patterns for 20 years on center fire but specific weighting has to be done so it may not be seen easily. You would be amazed how closely they resemble rimfire with respect to muzzle weight , I suppose it depends on how you look at the bending. I have a ladder test that I developed and scaled it to what I needed to see even the smallest of angular changes in highly controlled conditions. These patterns can be changed as well to a flat line pattern or a saw tooth pattern or tracking down at a specific rate or a standing wave. Here is a last adjustment in to a pattern that is needed for extreme range on my competition rifles. This times the standing wave to the exit time or velocity that would be on the in the middle of a smooth upswing of the barrel . Before the adjustment the standing wave had ripples in it so we get rid of the ripples to create a smooth consistent upswing.

 

[Jim Boatright]

Centerfire rifle barrels are bent upward by their attachment to the action during recoil. This initial displacement is not quite what I mean by a "vibration." It is the externally forced initial distortion which causes subsequent standing wave vibrations after that external force ceases. Just semantics, I guess. The attached rifle barrel "knows" its mechanical vibration modes even when they have not yet been excited. This recoil-induced transverse vertical distortion of the barrel does assume the general shape of one of the modes of subsequent transverse shear-wave vibrations (but not exactly that Mode 2 shape). There are many other types of shear-wave vibrations, as well as higher-speed acoustic vibration modes, all of which occur simultaneously and additively in the steel barrel material.

We always shoot "ladders" during load development as formalized by Creighton Audette in articles written for Precision Shooting Magazine about 20 or 30 years ago. You vary the barrel dwell time and hence the instant of bullet exit from the muzzle via incremental variation of powder charges. Our wind-free, mirage-free indoor 105-yard range removes some of the confounding variables encountered outdoors. The powder charge where successive shots group together at 105 yards identifies the bullet exit time when the muzzle is vertically stationary relative to the fixed earth below it. Any subsequent barrel shortening or rigidly attaching any mass to the muzzle will change this desirable exit time. Any change in the load or bullet seating will also change the barrel dwell time and thus the bullet exit time.

Due to longer barrel dwell times, rimfire rifles generally do start freely vibrating before bullet exit. The long, slender barrel of the old MkIII SMLE was also perhaps an example of this due to its very low base pressure at bullet exit. Distortion amplitudes are greater for the more flexible slender rifle barrels. Fundamental mode frequencies are also lower for more flexible barrels. Modern, heavy barrelled, high velocity rifles can only typically use that first instance when the downward bending speed of the muzzle matches (and cancels) its upward recoil motions. The chamber pressure curve for a modern shoulder-fired rifle looks like the first half-cycle of an 800 microsecond driving cycle, indicating a peak in the vibration driving spectrum at about 1250 hertz. Vibrational energy transfer to the barrel in Mode 2 (single node) transverse vertical vibration can be minimized by shifting its Mode 2 resonant frequency well away from this dominant driving frequency.

 

[timintx]

Centerfire rifle barrels are bent upward by their attachment to the action during recoil. This initial displacement is not quite what I mean by a "vibration." It is the externally forced initial distortion which causes subsequent standing wave vibrations after that external force ceases. Just semantics, I guess. The attached rifle barrel "knows" its mechanical vibration modes even when they have not yet been excited. This recoil-induced transverse vertical distortion of the barrel does assume the general shape of one of the modes of subsequent transverse shear-wave vibrations (but not exactly that shape). There are many other types of shear-wave vibrations, as well as higher-speed acoustic vibration modes, all of which occur simultaneously and additively.

We always shoot "ladders" during load development as formalized by Creighton Audette in articles written for Precision Shooting Magazine about 20 or 30 years ago. You vary the barrel dwell time and hence the instant of bullet exit from the muzzle via incremental variation of powder charges. Our wind-free indoor 105-yard range removes some of the confounding variables encountered outdoors. The powder charge where successive shots group together at 105 yards identifies the bullet exit time when the muzzle is vertically stationary relative to the fixed earth below it. Any subsequent barrel shortening or rigidly attaching any mass to the muzzle will change this desirable exit time. Any change in the load or bullet seating will also change the barrel dwell time and thus the bullet exit time.

Due to longer barrel dwell times, rimfire rifles generally do start freely vibrating before bullet exit. The long, slender barrel of the old MkIII SMLE was also perhaps an example of this due to its very low base pressure at bullet exit. Distortion amplitudes are greater for the more flexible slender rifle barrels. Fundamental mode frequencies are also lower for more flexible barrels. Modern, heavy barrelled, high velocity rifles can only typically use that first instance when the downward bending speed of the muzzle matches (and cancels) its upward recoil motions. The chamber pressure curve for a modern shoulder-fired rifle looks like the first half-cycle of an 800 microsecond driving cycle, indicating a peak in the vibration driving spectrum at about 1250 hertz. Energy transfer to the barrel in Mode 2 (single node) transverse vibration can be minimized by shifting its Mode 2 resonant frequency well away from this dominant driving frequency.

Ah , OK , I apologize I misunderstood. I certainly meant no disrespect. I have heard that before and just wanted to show the bending of the barrel is possible while the bullet is still in the barrel because it is what I have to prove to the military and others that doubt there is bending or that positive compensation in rifles even exist. I also have to prove I can change ,structure and control it which is a tall order to those that have their mind made up already. I think the term vertical bending under recoil is the safest explanation to describe what I am doing so I agree with your explanation. The patterns I showed in these ladders were difficult to obtain at the time but now not so much because of the years of comparing patterns to the correct variables such as weight offsets above and below bore center line , recoil force and flexibility in both the stock and barrel and muzzle weight . Shooting extreme ranges I have to have some mechanism in place to reduce vertical dispersion for extreme ranges due to velocity variance. With these patterns I use to accomplish that they are still hard to prove at 3000 -3600 yards unless there are perfect conditions. if I were shooting inside of 1000 yards I would structure the bending to be flat on the line with all charges which makes for great 100 yd groups but would fall out at the more extreme ranges with the slightest velocity variance especially with cold bore shots . By picking a charge in the middle of the upswing {93 grains of powder] I am converging differing velocities down range reducing vertical dispersion at approximately 800- 1000 yards and beyond that point. There are ripples within the upswing that I thought could not be eliminated as well but turns out they can which makes it possible to use the bending for a rifle to shoot better at extremely long ranges . As I am sure you know barrel vibrations and related movements have always been a controversial and is a subject and I catch heck because of it trying to show positive compensation is possible at long and short ranges with a military rifle with unknown amounts of throat erosion , with 60 fps extreme spreads it will only shoot minute of barn at 2000yds. They can not get past 1760 reliably with most rifles now. This weekend using this structuring of this long range pattern I was able to get a cold bore first shot in competition at 2913 yds with minimum drop due to being slower on the cold bore shot . I do not think it would be possible with a extreme spread of 30 fps which is what my cold bore velocity is over the normal second shot velocity and that mixed in the velocity variance even more unlikely to hit a 36 inch plate.

Thank you for the reply , I hope I did not detract too much from the original post.

 

[Jim Boatright]

After getting the base drilling of our monolithic copper 338-caliber bullets right, we have seen many 5-shot groups with extreme spreads of muzzle speed around 4 fps. That is in 338 Lapua Magnum using VV N570 and Federal 215 primers. We saw this in both Schneider P5 7-inch twist and Bartlein 5R 6.6-inch twist test barrels. Gary Schneider's P5 rifling is the best rifling pattern we have seen for allowing the bullet to seal the powder gasses completely. Conventional match-type rifle bullets made with soft lead cores should do just as well.

Barrel obturation is aided by making the rear driving (and gas sealing) band slightly over groove ID at 0.3383-inch and by base drilling at 0.1520-inch ID up to about half way under that RDB. Porting the base pressure internal to the gas sealing band is necessary for any monolithic copper bullet design to be able to prevent gas leakage during firing. Any larger RDB diameter, and the engraving forces and shot-start pressure go sky high. Much larger base drills will cause mechanical failure of the bullets at extreme spin-rates. The base drilling does cost about 10-grains in copper bullet weight but the firing uniformity gain is worth it. Base drilling also slightly shifts the CG forward and reduces the over-large ratio of transverse-to-axial second moments of inertia (Iy/Ix) for these long 6.2-caliber copper bullets, which improves the overall mass distribution of the projectiles.