BudsGunShop.com - What makes a gun +P rated?

the manufacturer tests the gun with +p proof loads and decides it is safe and that they cover any warranty issues rising from the use from the higher pressure loads

Bradley, a +P rated firearm has been "Proof" Tested at the factory to ensure the design will stand up to +P rated ammunition for a sustained period of time. Target ammunition is usually not +P and is usually shot in greater numbers than more expensive +P Premium Self defense Ammunition. You don't have to worry about Magnum revolvers such as 44 Magnum, 357 Magnum etc, as they are built to handle the more powerful magnum loads from the onset and the +P 38 Special and 44 Special are nowhere close in pressure to their Magnum counterparts.