Lots of complicated/complex info. so far. But, for all intents and purposes, the only difference in +P and standard .38 Special brass is the headstamp. I wondered about this around '86 and I weighed mebbe 100 mixed .38 cases. "Blind test"; I would place a case on the scale without looking at the headstamp, and wasn't able to determine which was which with any consistency. Some .38 manufacturer's brass is heavier than others, but I was not able to determine the maker buy weight as even the same manufacturer's brass would vary up to 1.5-2.0 grains, untrimmed (different lots?).