It'd stabilize anything from 40 grains up to I'd say about 70 grains, but the best shooters would probably be in the 55-62 grain range. One of the things to watch out for with lighter .224cal varmint type bullets, in fast twist barrels, is the possibility of driving them so fast that the centrifugal force on the jacket causes the bullet to expand and tear itself apart in flight. Many of these bullets are designed to stay together with the more standard 1-in-12 rifling. The heavier bullets shouldn't be a problem because the velocities are lower.

Mike