Unsure if I should post this here or under gunsmithing but anyway.
I'm hopefully soon getting a 50-110 built and the barrel I have is 1:12 twist.
A fellow poster here has one with a 1:26 twist, and is getting the velocity I want to achieve.
So will the big difference in twist rate cause an increase in pressure over and above the normal difference between 2 chambers?

Supposedly, very little (1% or less) of the combustion energy is used/required for twisting the bullet. I don't know that you could tell the difference, all else equal.

Regards, Bill

There is an Internet Myth that faster twists equal higher pressure and lower velocity. At 50,000 psi, I can assure you that the bullet is not going to slow down coming out the muzzle. It made shred the jacket with extreme twists rate (1:5), but in any event the bullet is coming at the same velocity based upon charge weights.

Reducing bore friction with moly does have an effect on velocity - it generally reduces pressure and velocity. Other than reducing bore friction, twist has little effect on internal ballistics.

One of the theories of gain twist was that it reduced pressures since it started out slow. But since nobody uses it now that tells you a lot about that theory. Besides I always thought gain twist would tear up the jacket a bit which wouldn't help accuracy.

OK thanks guys this means I don't have to go out and find another barrel which is good news.
Thanks again.

416SW,
The very smallest difference in bore diameter will affect your velocity more than any change in rifling twist rates. There's no guarantee that your barrel will get the same velocity but you won't be able to blame it on the rifling.

PaulS

Thanks Paul