Ask Ian: Progressive Twist (Gain Twist) in Small Arms?

From Jamie on Utreon:
“I know naval gatling guns like the 20mm CIWS uses gain twist rifling, but are or were there any commercial or military small arms that used gain twist rifling?”

Yes, there have been some significant uses of progressive (gain) twist rifling on military and civilian small arms. These include:

Colt percussion revolvers (1848, 1849, 1851, 1860, 1861 models)
Custom barrels for Sharps, Stevens, and other rifles by Harry Pope
Carcano Model 1891 rifles and carbines
S&W .460 XVR revolvers

There are certainly others, but those are some of the most significant.


  1. Folks on another site were just discussing fast-twist barrels for very long bullets optimized for suppression. That seems like it might be a logical application.

      • Daweo,
        Thanks for the link. I should have written more clearly. I was specifically referring to cartridges that extrapolate the .300 Blackout philosophy to the AR10 platform. Because they use very fast-twist barrels to stabilize long, heavy bullets, some speculate that they may not work with the low end of bullet weights (and therefore not be versatile like the Blackout). I was suggesting that gain-twist might be an effective compromise to stabilize a very broad range of projectile weights.

  2. Gain twist was necessary in blackpowder days. Lead bullets were launched into the barrel by the sudden pressure peak of black powder combustion, attaining full velocity in the first ten inches of barrel length.

    A slow twist at the leade’ was necessary to avoid the lead bullet stripping and not fully taking the rifling. The tighter twist further on increased bullet RPM and thus improved downrange stabilization.

    The advent of jacketed bullets and smokeless powder in the 1880s rendered gain twist largely obsolete. Smokeless powder can be formulated to generate almost any pressure curve you want, resulting in a more gradual acceleration in the barrel, and properly-made jacketed bullets don’t strip.

    Other than arms intended specifically for use with black powder, the use of gain twist in modern production arms is something of an affectation. Mostly, it hangs on simply because “it’s always been done that way”.



    • Gain twist was never necessary for black powder. It was seen as beneficial by some but truth is this was marginal at best.
      But whatever improve your confidence in your gun makes you shoot better, so its psychological value is not to be thrown away.

    • You are incorrect. Where you need to shoot varied bullet weights or shapes all accurately and to the same or near same POA, gain twist is ideal.

    • I thought black powder burned slowly and built up pressure slowly, which is why barrels were so long.

  3. Seeing bullet’s progress thru red hot barrel made me understand how bullet progresses thru it. It starts slow so you can for fraction of second follow its movement.
    That makes me think that if the bullet moves slow, it also spins slow. Thus progressive rate of twist sounds to me as moot point. Issue is off the table for most part. That is for small bores; for something like 3″ artillery barrel it may be a different story.

    However, my respect goes to those who spend so much effort to address it as valid and useful. Again it shows that practice often trumps theory.

  4. In the early development of smokeless powder and jacketed bullets, there were too many unknown or undefined variables in pressure and different jacket materials to say “Yes we have the correct formula for every possible scenario of how x bullet jacket and z powder are going to interact until we put the two together and see if the gun blows up.” Also, early smokeless barrel steels were inconsistent in quality and uniformity of composition. This is why you cannot absolutely say “x bullet plus z powder in the 6.5 whichever cartridge is going to give absolutely identical results every time.” Add to those variables in chamber dimensions and hardness of brass cases and early priming compounds and come up with perfectly repeatable results in every single situation. Also, I recommend an editorial by Dave Andrews called “Why Ballisticians Get Gray” on the variables within one caliber/cartridge are more a function of the guns used to test the ammo in question than of the ammo itself. This was first published in one of the older Speer reloading manuals but is probably available online now.

  5. Hi Ian , A real quality answer! Now I have in my stuff an old artillery piece (with gain twist rifling) It is an English “15 pounder” dated 1903 it is one of the last fieldpieces with fixed trunnions (like a cannon) .as this allows the recoil to drive back the gun firing was a pretty fun activity , made all the more fun by the method of firing >>a large brass pistol grip which is part of the actual breech block it fires a blank >577/450 igniter round into the main charge ( it is NOT a cartridge loader ,shell & propellent load individually ) the breech is not the usual sliding wedge but a pretty complex rotating mutilated screw idea,I think the Brits of the time were trying to praise up their mechanical expertise In place of sliding recoil absorbing designs it has a sort of “fishtail” spade that supposedly digs into the ground & a spring cable supposedly takes care of the recoil (remember the gunner is ahangin onto the brass pistol grip Yee Haaa) Anyways back to the RIFLING it is also RATCHET GROOVIG style. your comment on large mass “bullets” is very well made…. love your excellent material make 81 yr old days better!

    • Accoring to British usage, an artillery piece firing seperate loading ammunition (projectile with separate powder charge) is a Breech Loader and a weapon using fixed or semifixed ammunition (projectile and powder charge in a common casing – like a giant rifle round) is a Quick Firer. The breech is known as the interupted thread type and was (and is) used around the world on all caiber of weapons, the alternative is the sliding wedge type. Debate has maxed hard and long over the years as to which is superior, with much ink spilled in vain. The 15 pounder Mark III was a hurried botch job for the Boer War. The British Master General of the Ordnance had his minions develop not one, but two possible replacements, the 13 pounder (3 inch = 76mm) and the 18 pounder (84mm) and asked the Royal Regiment of Artillery which one it wanted. It couldn’t make up its mind, going higher and higher up the chain it went, until in 1904, it was dumped in the Prime Minister’s unwilling lap. True to the spirit of British Compromise, he said let’s have some of both. It actually turned out to be an inspired decison. The lighter and easier to maneuver 13 Pounder was given to the Horse Artillery to accompany the cavalry (King’s Troop RHA still uses theirs to fire cereminial salutes in places like Saint James Park). The 18 Pounders went to the Foot Artillery to back up the infantry. Due to the nature of WW1, the number of 18 Pounders – “the standard field gun of the Empire” – greatly outnumbered the 13 Pounder, although some of the later were converted to AA pieces to defend London. And byt the way, the American 75mm Gun M1918 was a US built 18 Pounder converted to 75mm. And what of the 15 Pounders, you ask. “The Ordnance BLC 15-pounder gun (BLC stood for BL Converted) was a modernised version of the obsolete BL 15-pounder 7 cwt gun, incorporating a recoil and recuperator mechanism above the barrel and a modified quicker-opening breech. It was developed to provide Territorial Force artillery brigades with a reasonably modern field gun without incurring the expense of equipping them with the newer 18-pounder. The weapon was used by British Territorial Force, New Army and Canadian infantry divisions in all theatres of World War I until replaced by the 18-pounder from 1916 onwards.”

  6. The bullets used in Colt percussion revolvers had short driving surfaces for rotation, this is obvious in the case of round balls and I think that it also applies to the style of conical used in these revolvers. Thus there is a better case for the usefulness of gain-twist rifling than in later weapons use bullets with longer driving surfaces. Many artillery shells have steel cases which ride on the lands and narrow brass bands for sealing and driving rotation which would again allow gain-twist to be advantageous.

  7. Is gain twist common with artillery? I don’t know much about land artillery, but naval shells have a driving band to engage the rifling.

    • The actual shells of land based artillery are quite similar to naval ones, driving band and all.

  8. A lot of research was done by Mauser during the war on this rifling and the result
    seems to show that for 20mm and 30mm there was a large increase in barrel life but not
    so much in 8mm. Today the Aden (Mauser 213) is progresive twist

    • There are exceptions of course, but pretty much all cannons starting at 20 mm and then up have gain twist (or progressive) rifling. Most handweapons do not.

    • Mostly to even barrel wear. The original balistite load, with constant rifling, tended to wear more the throat of the barrel than the muzzle. Progressive twist, evening the wear prolonged barrel life.
      The new solenite load, adopted in 1896, reducing flame temperature, generally further prolonged barrel life, but made also so that, with progressive rifling, the muzzle tended to wear more than the throat. At that point progressive rifling was no more useful, but the specs had already been made, so it was retained.
      The progressive rifling had been abandoned with the first Carcano model designed after 1891, the 91/28TS.

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