Gain Twist Rifeling

[draken]

I understand what gain twist rifling is, but I'm curious to know what the benefits might be.

Thanks,
draken

[heinz]

The concept behind gain twist rifling is the ball is started spinning lowly without an abrupt jump into the 1 in 44 (or whatever) twist.  This could prevent a tendency for the ball to slip or twist in the rifling at the very beginning of its trip down the barrel.  The contrary opinion is that you have already swaged the rifling into the ball when loading, if you load tightly enough.

Because the ball accelerates from a dead stop to 1000 fps and more in its trip up the barrel, the rate of spin is always increasing, even in a standard twist.  Maybe the gain twist helps, I do not know. 

Folks who have Hoyt gain twist barrels, like them.  I have a Bobby Hoyt  barrel I am building right now that is  #0791, marked 50 cal 1:63  but I think that is straight twist.

[Bob Roller]

The gain twist was used by the makers of the most accurate muzzle loading rifles of the percussion era and was also used by makers like Harry Pope whose rifles worked best when loaded thru the muzzle.The initial push by the ignition of the powder charge was taken advantage of by the compression build up as the projectile finished the journey thru the bore.The rifles of N.G.Whitmore were,according to Ned Roberts declared as unfair competition and not allowed in some shooting matches in New England.Gain twist and 12 grooves worked well and I am wondering why a modern maker hasn'f looked into the Whitmore system.I tried to talk Bill Large into it be he showed no interest even when he had a Whitmore barrel in his shop.The 38 caliber Whitmore rifle made for General Grant was tested at 110 yards and put 10 shots into the diameter of a percussion cap box without the telescope sight so the idea does work.The early and much feared 88MM gun used with devastating effect in WW2 had a gain twist but reverted back to uniform spiral as time went on and the war was being lost by Germany.
Bob Roller

[L. Akers]

As has been stated, the gain twist reduces the chances of stripping the bullet.  It allows a larger powder charge for increased velocity (flatter trajectory) without stripping.  The constantly changing angle of the rifling provides better obturation of the bore.  Gain twist produces less torque as the bullet starts to move.  This last is why I rifle my target pistol barrels with a gain twist.  The gun won't move as much.

[Daryl]

The ultimate gain twist, was called paradox rifling. From zero, to 30"(last 3"-4").

[Dphariss]

I understand what gain twist rifling is, but I'm curious to know what the benefits might be.

Thanks,
draken

There is no reverse gain for one thing. I don’t think this was all that important with the round ball but when the picket bullet and long cylindrical bullets came into use a rifling guide with a slight reduction in twist at the muzzle will cause accuracy problems. This is MY theory and its worth very little. But I think its a viable idea given how many rifling guides were made back in the day at least  up till the  American Civil War. Though I suspect that some really serious rifle/barrel makers likely had iron/steel guides by the 1830s-40s.
I don’t think that a gain will out shoot a straight twist so long as the straight twist is uniform end to end. Of course meaning all things are equal. Uniform hardness in the bars of steel, care in reaming and rifling etc. But gain twist barrels DO shoot really well with RBs or bullets. But then straight twists will as well .. So??? The only dedicated ML match rifle I own has a gain. But it would take a lot of testing with a lot of barrels to prove it.
The other thing is the secrecy that a lot of makers adhered to.

[alacran]

All this was hashed out in the 19th century. If you want a good explanation of the subject, Ned Roberts covers it very well in his book.  He also says that the debate about which is better was going on well into the 20th century, with no conclusive answer as to which is better.

[recurve]

I have 2 Bobby Hoyt barrels one 1-56 and a gain twist both shoot great. the advantage of the gain twist is the ability to use conical bullets and patched round balls out of the same barrel( Bobby claims a speed increase over standard rifling)
gain before sight adjustment to the left, sight moved center hit

1-56 twist rifling before sight adjustment

[newtire]

I know that this is done but can't wrap my thinking around how the rifling can start out engraving into the bullet at one angle and then change angle of twist as it moves down the bore without scrubbing away part of the bullet.

[Dphariss]

I know that this is done but can't wrap my thinking around how the rifling can start out engraving into the bullet at one angle and then change angle of twist as it moves down the bore without scrubbing away part of the bullet.

Bullets with long bearing surfaces have been proven, in modern times, to be best with only about 1/2” gain. I.E. from 20” to 19.5” for example. Higher gains as used for RB barrels or short bearing surface bullets like the picket result in “skid marks” on the bullets. I dare not say more or some here will have their hackles rise.