Once you hit a certain point, most of the extra powder is burnt in the air just outside the muzzle adding only to the smoke cloud. There are a lot of factors that determine that ‘certain point” e.g. primer, powder, gas seal, projectile weight, etc.
I don’t think anyone can pinpoint the specific point at which this happens for all rifles, all loads. Could be 70 for one load, 150 for another.
