Help with Ballistics and Twist rate

[Keith2324]

Hi folks. I need some help with ballistics and slugs.

I have gun D shooting a given slug at 926 fps with a twist rate of 12. I'm getting hole-in-hole at 30 yards and can consistently hit a 2 inch spinner at 100 yards with no effort. Gun F is shooting at the same speed but with a twist rate of 24 and getting 1/2 inch groups at 30 and 50 yards, but won't hit the broad side of a barn at 100 yards. I know all barrels are different, but as a basic measure, should gun F be shooting faster or slower for the slug to stabilize? I know some guns will not like certain ammo. But I'm just trying to figure out if more twist in the barrel means more or less speed. I hope this makes sense.

Thanks.

Keith.

 

[dannya1a]

faster the twist (lower Number) the more the slug will spin. In this case you listed the above. the 24 twist will have 1/2 the spin as the 12. you'll probably find better luck pushing the 24 twist slugs a bit faster.

 

[theLBC]

sound like F is not getting the slug to a high enough spin rate to be stable. you can try to increase the velocity, or try a lighter slug.

https://www.accurateshooter.com/technical-articles/calculating-bullet-rpm-spin-rates-stability/

 

[Keith2324]

Thanks. I will give that a shot. As far as weight is concerned, I'm as low as I can go with .22 slugs. Don't you just love testing?

 

[Brent]

Yeah you need to speed that 24 up to stabilize the slug . You didn't state barrel length so let's just say both barrels are 24 inches. Gun d slug will make 2 full turns before exiting barrel and gun f slug will only make one full turn before exit. My barrel is 17.7 twist so that's one full turn In 17.7 inches. 

 

[Greg_E]

You could shoot bismuth or tin slugs, which would be a lot lighter, but might not be what you are looking for.

 

[Guest]

The rate of twist needed is calculated by the length of the slug. Shooting at a higher velocity will increase rpm speed to some degree but often not enough for long-range.

Longer slugs need more twist to stabilize. So lighter slugs (of lead) will be shorter and require least spin unless they are extremely hollowed out and longer.