Stick with standard ammo in the WWII P-38.
These guns are aging now, and many were heavily shot over the years.
In addition, the Bakelite grips are aging and getting fragile. Hotter ammo could stress crack or break the grips.
There's no sense in over-stressing and possibly damaging a collectible.
Wanna shoot HOT 9mm ammo, buy a modern gun MADE to shoot hot ammo.