Steve, there are several issues related to guns that I know a little about, this issue, I know a lot about. Not only have I worked on it professionally, but it is a hobby too. I used several methods to measure pressure including Oscilloscopes and FFT, transducers, strain guages, piezo electroincs, etc. I never saw peak pressures deviate by more than 2000 psi round to round and with jacketed, no more than 1200 psi round to round. 5,000 psi variations imply large velocity variations on the order of more than 100 fps. That is way too much. When I quote numbers, I have used conventional statictal methods or standard mathematical analysis to determine them. I started out with a 33,000 psi round with a std dev of 719 psi. After 500 rounds with jacketed bullets, the pressure was 33,000 with a std dev of 823 psi. After 50 rounds with lead , 34,200 psi, 100 rounds 35,100 psi, 150 rounds 38,800 psi, and at 200 rounds 41,000 psi, 300 rounds 45,000 psi. The last few started to have greater std devs approaching 2000 psi, but the results are still statistically accurate. Notice this is NOT linear. Also the velocity started to climb at about 5 rounds fired, by 50 rounds it was 40 fps higher than the first round. By 100 rounds it had climbed by about 90 fps. At 150 rounds, 80 fps higher and at 200 rounds it was about 30 fps higher. Velocitites are all averages with no std dev exceeding 30 fps. Also, realize that this was in controlled conditions with each charge hand weighed, and tight chambers in pressure barrels. Hope this satisfied your curiosity. Good Shooting, MarkCO