Understanding Gain Twist

[nick338]

Have been reading up on the subject, specifically Frank's posts from last Feb. It's described as being more forgiving for the jacketed projectile which is great for obvious reasons, but I'm having trouble understanding how. If I'm correct in saying that bullet rpm is the main enemy I understand that not torquing the bullet right off the bat at the breech end is beneficial. What I do not understand is the bullet is accelerating all the way through the bore until it exits the muzzle so if the twist starts out slow but gradually becomes faster towards the muzzle the bullet rpm and velocity are still peaking at the same time. How is this avoiding the negative effects of over-spinning a jacketed bullet if the rpm is still reaching an undesired level?

 

[Matthew488]

As I understand it a gain twist barrel allows for a more gradual rotational acceleration of the bullet. However the twist rate at the muzzle combined with muzzle velocity will still determine the rpm of the projectile. So if both barrels end in a 1 in 7" twist and have the same velocity the centrifugal force will be the same. The gain twist will just get there more gradually with less torque applied during initial acceleration.

 

[nick338]

As I understand it a gain twist barrel allows for a more gradual rotational acceleration of the bullet. However the twist rate at the muzzle combined with muzzle velocity will still determine the rpm of the projectile. So if both barrels end in a 1 in 7" twist and have the same velocity the centrifugal force will be the same. The gain twist will just get there more gradually with less torque applied during initial acceleration.

Correct so is it the initial torque that disturbs the jacket the most or is the peak rpm after the bullet leaves the muzzle that is causing jacket and core issues?

 

[AIAW]

I posted this a little bit back regarding the subject. It's minute, but an advantage none the less.

https://www.snipershide.com/shooting/threads/alternative-twist-barrels-progessive-lh.6922043/

 

[nick338]

Just had Bartlein switch my barrel to a LH 9.75-8.75 gain twist at their recommendation for the 300 PRC build. They advised to keep it at 1" of gain.

 

[badassgunworks]

jacket and core damage is caused early when engaging the throat if you easy your way into the spin rate ( rpm ) it allows the stress to be less abrupt. Now gain twist will cause a wideer land pattern on the bullet that will lower bc due to bullet damage . if the bullet has less jacket damage from stress perhaps it will hold togather thats the only benefit to a pregressave twist barrel and perhaps a little more muzzle velocity can be obtained as well.

 

[leftyk82]

Just had Bartlein switch my barrel to a LH 9.75-8.75 gain twist at their recommendation for the 300 PRC build. They advised to keep it at 1" of gain.

And, for anyone interested, Bartlein charges a premium for gain twists barrels greater than 1 inch. (sample size of my one order, so I'm assuming here)

 

[nick338]

And, for anyone interested, Bartlein charges a premium for gain twists barrels greater than 1 inch. (sample size of my one order, so I'm assuming here)

Mine was an extra $40.00 for the gain twist but I can't comment on what it would be if it was greater than 1" as we did not discuss it.