After I wrote about about +P ammunition a while back, there were several reader responses. For that reason, I have dug into the matter again to come up with more data on the subject. The term +P is associated with certain handgun cartridges. It essentially means “loaded to greater pressure.” In the strict sense of the word, the term belongs to SAAMI─Small Arms Ammunition Manufacturer's Institute. SAAMI technicians have determined that four pistol cartridges─.38 Spl., .38 Super, 9 mm Luger and .45 ACP─may be loaded to a certain higher pressure levels and sold, as long as they are marked “+P.” Note that .45 Colt is not a SAAMI-sanctioned +P cartridge. Some readers have mentioned that a popular internet information source says that it is, but the latest listings from the SAAMI are to the contrary.
Apparently, some unknown number of small ammunition makers are in fact offering .45 Colt ammo that bears the +P stamp and box label. In view of the fact that certain of the handloading manuals actually list high pressure .45 Colt loads for use in Ruger and Freedom Arms revolvers, you can sort of see where these makers are coming from. If this kind of hot stuff is used in other, probably older revolvers, the guns stand a good chance of catastrophic failure. I can well understand the drive to build a more competitive product, but when their +P loads are not in accordance with the specific pressure levels SAAMI lists for use with the “+P” label, there is no way to identify what they are. This means you should approach the matter with extreme caution.