Surrell, I enjoy responding to your questions, although I do not have very knowledgeable answers. I would think ‘peak pressure’ could be determined by observing primers and noticing bolt lift. These two should at least let you know when you are getting close. As far as barrel length, not sure, but would think it to be minimal.
If anyone is interested in watching how a rifle barrel performs, Doug Pugh has a 31″ barrel on a bench gun and if he shoots it this weekend at Reese Bottom, I will try to remind everyone to watch. Most of you know where I observe the firing line from and two months ago as Doug was shooting I noticed for the first time ever how the barrel responds once fired. That thing whipped like a fly rod. Pretty interesting and the thing shoots ‘lights out’. Thanks, WWE