I've been reading about gas checks, and I'm a bit confused. From what I've read, it seems that the critical factor in using a gas check is velocity, and that the purpose of a gas check is to prevent gas cutting. Now, I don't understand why a higher velocity increases the risk of gas cutting, I would think that pressure would be the key ingredient (assuming the bullet is sized correctly), ie if it exceeds the yield strength of the lead and "pushes" its way around the bullet or something. If you are pushing a 9mm bullet at 1200 fps and 35,000 psi or so... why does that not require a gas check when pushing a rifle bullet to 2000 fps under the same max pressure does? With the gas check you still have mostly lead on the sides of the barrel, so it can't be the increased friction.
Anyways, the point is... I don't understand why you need gas checks, or at least why they seem to be velocity dependent. Can someone please explain this to me?