Methinks you may have it backwards, 4227 is slower than 2400, especially these days when 2400 is even faster than it was 30 years ago. You're right about the burning rate affecting the blowback action, the slower powder gives a slower & thus longer-acting shove necessary to keep the heavy breechblock moving back far enough to cycle the action. It's not an exact apples-to-apples comparison but it does point out some of the effect of a different burning rate. The 2400 slap doesn't last long enough to move the block far enough but I'll bet that repeated use of the fast 2400 load would eventually batter out the breech face while the slower 4227 load would not be as damaging. Again, JMO.
Regards, Joe
