I have a 637 J-frame Airweight in .38 Spl.+P and just bought an older 64-3 K-frame that says .38 Spl. on the barrel. I'm wondering if it's a bad idea to shot any +P ammo through the older K-frame? When did they start using +P ammo and rating guns for it? Also, if it's a matter of strength, how can they make a little aluminum J-frame stand up to +P ammo and not have a solid steel K-frame not be able to handle it? I appreciate any tips you can give me. For now, I'll stick with what is printed on the barrels. I haven't ever even fired any +P ammo through my 637, but I do have some for carry. I really need to fire a cylinder's worth to see where POI is vs. POA with that ammo if that's what I'm going to carry now.