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gain twist rifling   General Military Discussion

Started 9-Aug by smg762; 3190 views.

From: roguetechie


There's some interesting ndia presentations involving flow forming such liners showing quite a bit of promise.

That presentation was several years ago too, I imagine it has progressed significantly since then.


From: smg762


Well my pet project was a 6.5mm bullet , not 6.7mm, with 300 win mag energies.

To achieve it the barrel is 29 inch, totally smoothbore for 9 inches and then a very slow increase to the full rate.  Full rate only starts at the last 8 inches.

So it's basically a smoothbore gun. Then u add the drive bands and stuff.

For recoil i was thinking a moving stock, like the FG42. Optic violently recoils too, so you keep your needs a long eye relief.

Any thoughts on this concept? A 90 grain VLD at 4000fps...

In reply toRe: msg 8

From: ZailC


Why bother with the far-end, gain-twist rifling? Spin energy is well less than 1% of  muzzle energy: negligible savings and incredible loads on driving bands. Heavy gilding copper may not take your loading, lexan will not, sintered/fused iron is a maybe/maybe not. Small-bore, long barrel, great energy: a large portion of it in the 60-70 grains of gas following the projectile out the muzzle. Barrel wear might be a concern. 

In reply toRe: msg 9

From: smg762


Type in 308 smoothbore 5000fps, and theres a vid of a guy who achieved somethig somilar...i cant load it so didnt see the bullet weight.

Also theres a russian smoothbore gun TS2, with paradox rifling.....whats that

Lastly ARL apparently got 5000fps out of a taperbore AR, with 100k PSI 

Could one have he full twist rate only on the last 6 inches of barrel....or is that not enough.


From: JPeelen


You seem to think that using a smooth bore is a necessary condition to achieve extremely high velocities. This is not so. The tank guns started using smoothbores because of the necessity to launch extremely long penetrators. For reasons of gyro physics, these long projectiles simply cannot be stabilized by spin. That is why smoothbore came into play. 

So far, nobody has been able to achieve with smoothbore small arms a target dispersion comparable to that of rifled small arms. Five to ten times larger small arms dispersion is typical. 

If you would do even the most simple and trivial research before posting questions, you would have long found out that paradox is a very old way of trying to improve slug dispersion from shotgun barrels. Tried hundreds of times, never a success. 

Your proposal of starting with a bore rifling of 0 degrees which increases to the necessary rate of twist has been in daily routine use for decades, for example in the German 27 mm aircraft cannon of the Tornado and other aircraft. Starting the rifling not inf front of the chamber but some distance down the barrel (hopefully with the projectile already very fast) would introduce a BIG transient in the entire physics of barrel movement. In my view, it is a recipe for BIG dispersion.  

The general rule in armament is that our modern smart ideas of improving are never new. They have been tried already a century or two ago. In some cases, available technology and materials of the time prevented success. But the mechanically unsound like paradox are today as useless as they were long ago.           

  • Edited 12 August 2021 14:33  by  JPeelen

From: smg762


Yes i should have clarified the idea was really for an infantry round, not an MG round so the dispersion should be fine with single shots. Again, its well proven that slower twist rates or no twist rates, will boost speed. So that was the logic...a 28 inch gain twist barrel to get 4000fps with a 6mm bullet.

Back with the GDs movig you think its an accurate gun or should hey have taken the FG42 approach

Quick favour...i cant load the video (or forum article on about the 5000fps 308. Could anyone tell me the gist of it worked

  • Edited 12 August 2021 16:29  by  smg762

From: ZailC


I don't see the long smooth-bore section of the barrel giving you a velocity advantage (one-percent is conceivable). Concur with JPeelen's points. A very late and short (about a single turn) rifling to achieve the desired spin rate for stabilization is problematic: extreme forces acting on projectile body/driving bands. Engraved portion would have to be very substantial to maintain integrity during late spin up. I imagine it would be quite akin to a squeeze-bore system. Barrel dynamics would be strange. A short freebore before rifling might have some advantage, but I don't see how.  Establishing the rifling lands and grooves soon after chamber exit gives the projectile a longer shaping period and minimizes working stresses on the grooved shell/driving band. Progressive twist rate is also problematic for much the same reasons. 

In reply toRe: msg 13

From: Farmplinker


Well, Roy Weatherby found some freebore  helped reduce pressure on his admittedly hotter rounds. He used way less than SMG is proposing, though.


From: EmericD


For someone who wants to duplicate .257 Weatherby ballistics, some freebore makes sense, but I'm still failing to see the military objective.

A .257" / 90 VLD launched at 4000 fps from a 29" barrel is probably a solution, but I don't see the problem the OP wants to solve (the M948 SLAP is probably what you want).