There are differences between .38 cases, but usually not between commercial .38 and .38+P or +P+.
However, Winchester has loaded a LOT of .38 for Uncle Sam, and it IS to a diffferent spec.
Particularily, the PCU-B ammo, originally loaded for the Air Force with a 130gr FMJ to approx. 1300fps from a 4" bbl (yes, nearly .357mag, and yes, I've chrono'd some my brother "retained" when he retired from USAF Security Police) that were essentially a +P+ and had considerably thicker brass than the usual .38special commercial ammo. Some lot's of this were profoundly accurate. My brother has his "leg" match from a civilian PPC Regional match he shot with it. With a box-stock Ruger Sec.-6, no less ! (requires using factory loaded ammo. Not bad for a Marksman class shooter).
The further downside is that the brass had the same knurled cannulure above a single thin ring turned into the brass, EXACTLY LIKE THAT OF THE .38spl W-W Super-Match.
I recieved a bunch of it in a lot of .38 re-manf. reloads aquired from Master Cartridge (predecessor of Georgia Arms). I had it get mixed in with my "stash" of W-W match brass. Ammo loaded in that brass shot like Sh## due to the excessivly thick brass and occasionaly wouldn't chamber. Try shooting a PPC match under time with a few "Gotcha's" like that in the "mix".
Needless to say, of the 40,000+ .38spl cases I have, only a few hundred have the W-W headstamp and the double cannulure............ and that's because I haven't taken them to a recycler.......yet !!
There CAN be a difference !!!!!