jamesr said:
That is not correct. The sig case is stronger (stronger than even the 40 s&w), and is designed to handle the extra pressure.
The reason pistol manufacturers won't certify their guns to work with "+p+" ammunition is because there is no way to know what "+p+" means. It isn't a standard with an upper limit.
Standard 9x19mm SAAMI MAP is 35,000psi.
For 9x19mm +p the MAP is 38,500psi.
Anything above 38,500psi is therefore not within SAAMI specifications. It's called "+p+" but it could be 39,000psi or 41,000psi or 60,000psi. Smith (and other gun manufacturers) can't control what you might put in your gun that's called "+p+" and therefore they warn against it.
However, it's silly to think that the big manufacturers like ATK, Remington, and Winchester are oblivious about building ammo. Their +p+ loads are loaded within specifications set by their respective companies. Suggesting that one of these huge companies doesn't know how to create a brass case adequate to containing chamber pressure is silly.
Now, will "+p+" ammo from these companies cause wear on your pistol at an accelerated rate? Of course. But the average person will never shoot enough ammo through his gun for it to matter. Would I recommend shooting 20,000 rounds of +p+ through the gun a year? Probably not, unless you're willing to pay for the extra maintenance and, eventually, replacing the gun earlier than you would shooting standard pressure ammunition.
At various times in the past I've carried Federal 9BPLE (115gr +p+), Speer 115gr +p+ Gold Dot, and Winchester RA9TA (127gr +p+) in Glocks, Berettas, and SIGs and never worried about it at all. I wouldn't worry about it in a M&P, either.