I have yet to see (or hear) of a test where peak pressure wasn't reached within a short distance after the bullet left the case and entered the rifling. Say 2" on average.
Beyond that the pressure starts dropping, due to the greater volume inside the bore behind the bullet. Have yet to see/hear of any test that showed a significantly higher pressure peak due to a faster twist. The biggie is the pressure required for the bullet to enter the rifling.
Thank you for indulging a kid from the short bus. I do get your point now. Could I paraphrase that as peak pressures tend to happen when the bullet hits the rifling (before twist can become a factor)? Makes sense to me, but I've not seen pressure curves expressed as Distance/Pressure. I've only seen Time/Pressure. I think Muzzle Velocity might be a better indicator for pressure caused by twist because it would be a product of pressure AUC. Peak Pressure as you note probably doesn't touch differences in rifling twist since it likely happens at the throat before the twist exerts it's effect.
