Thread: Stability for subsonic projectiles

Yes , you need a faster/tighter twist to stabilise the bullets , I think its to do with the rpm of the bullet , remember a say 175gr 30cal bullet at say mach 2.5 , is being spun at 2.5 times more than the sane bullet at just under mach 1 .

Its to do with not just the projectile weight but also to a lesser degree the bullet/shape/ , ie bearing surface exposed to the rifling directly , thinl say a VLD jacketed compared to say a flat based cast RN bullet , the cast will have 2-3 times the surface in contact to the rifling .

If you look at say the 30 cal , at say 2700fps , 175gr SMK , a 1-12 twist is fine , and if say you wanted to run subsonic ( and to compensate for reduced speed , you normally go as heavy as you can ) , then you would need say 1-7 twist for say a 240gr bullet at 1000fps .

If you have a bullet of the same weight , and ones a VLD shape & the others a less streamlined cast RN flat base shape , then the cast bullet with more surface contact with the rifling will be easier to stablilise in a marginal twist rate .

The other factor that can cause timbling is if the bullets contact the baffles inside your suppressor , due to either mis-alignment issues or in-correct twist rate to fully stablilise the bullet .

As you will see , its ticky .


Later Chris