An 8" twist (or even a 7" twist) will shoot 55 grain bullets just fine. We've done this with M-193 55 gr G.I. Ball ammo and achieved good accuracy. Some lots of G.I. M-193 have given 10 shot groups equal to Federal Gold Medal Match (69 gr) ammo. With too slow a twist, a bullet can be under stabilized (tumbles, key-hoes, or wobbles in flight); however, you can't OVER stabilize a direct fire weapon. Over stabilization is only a problem with indirect fire weapons (mortars, howitzers, or long range guns) where you want to have the projectile track along the curved flight path with the fuze always presented to the front of the flight path (and the impact point). An over stabilized projo would not roll over to follow the flight path and could land at the same angle as it left the muzzle (on its side on the ground without the fuze being hit). With a direct fire rifle, what's wrong with the bullet going perfectly straight?