Fred, keep an on the weights of your cases.  I've seen as much as a 40gr difference between some newer R-P, 30-40 Krag and some older REM-UMC, 30USA.  The older stuff came to me once fired, and some of them were obviously hot loads.  Perhaps someone stuffed the heavy cases with their usual loads and got some higher pressures.  Not much variation in the new stuff, generally less than 3 or 4 gr, but the older stuff was obviously two different lots with 30gr variation.