One thing that must be fully grasped here is that as normally used in high vs low pressure loads, we are almost always talking "Exclusively" of chamber pressure. A "low pressure" load ie low chamber pressure may or may not have a lower bbl pressure than a higher pressure load. "If" the same ballistics are acheived, ie for instance say 1 1/8oz shot @ 1200 fps, with one load @7,000 psi & another @ 9,000 psi then the higher pressured load would beyond a doubt have a lower pressure for the most of the rest of it's bbls length. The thing to remember here though is that this max variation is within a very short distance while the other is spread out over most of the bbl's length. Thus while we have this 2k psi variation within the first couple of inches of chamber, for the rest of the bbl pressure is likely less than 4-500 lbs. I really think that, with the possible exception of very heavy loads using a large amount of slow burning powder, the actual load has little affect on this type of burst. These loads would not necessarily show an excessive chamber pressure & would still peak within the chamber area but would maintain a slightly higher bbl pressure, though not one which would ordinarily be considered excessive or dangerous.
