[carguychris]

The +P and +P+ deals with the pressure the cartidge is generating. You will have to check your owners manual for the specifics regarding what your pistol will tolerate.

IIRC the S&W M&P manual warns that +P may cause premature wear, but does not specifically recommend against using it; however, there is a specific warning against using +P+.

Here are my thoughts about 9mm ammo, winnowed down to the basics:

• Regarding bullet weight, most FMJ practice ammo is either 115gr or 124gr, while most defensive ammo is 115gr, 124gr, or 147gr.
• You may find some defensive loads with bullets lighter than 115gr, but these are essentially specialty items and aren't very popular. The 9mm case will not normally accommodate bullets heavier than 147gr.
• There's a lot of debate on the Interwebz and the gun store counters about which bullet weight and load is best for self-defense. Some of the arguments are useful and based on facts, but many others aren't, and many debates break down into intractable and useless Ford vs. Chevy, Dog vs. Cat, iPhone vs. Blackberry vs. Droid, or Mac vs. PC-type bickering.
• THAT SAID: Most modern, premium 115gr-147gr JHP loads from name-brand manufacturers should get the job done. OTOH I recommend against frangible loads like Extreme Shock, Air Freedom, MagSafe, and others; most experts regard these loads as marketing gimmicks.
• You may find some ammo labeled "9mm NATO"; this is normally a +P load with a 124gr FMJ bullet, and is perfectly acceptable for practice use in your M&P. The headstamp will look unusual but should incorporate a "+" symbol inside a circle (this is the NATO military mark).
• 9x19mm and 9mm Parabellum are alternate names for 9mm Luger and are safe to use in your pistol. These names are more commonly used on European-made ammunition.
• Other 9mm ammunition (9mm Makarov, 9x17mm, 9mm Browning Short, etc.) is NOT the same and should not be used in your pistol. It is NOT SAFE, regardless of what the occasional numbskull behind the store counter may tell you.
• I recommend against using cheap Russian ammo, but not necessarily because of the steel cases; I don't like it because some of this ammo uses copper-washed steel jackets (which may cause premature barrel wear) and/or steel cores (which have an increased tendency to ricochet and/or penetrate shooting-range backstops; many public ranges ban this ammo for this reason).
• Unlike the Russian stuff, IMHO there is absolutely nothing wrong with inexpensive brass-cased and copper-jacketed ammo from Eastern Europe (namely S&B and Prvi Partizan; FYI the "Monarch" brand ammo at Academy is relabeled Prvi Partizan).
• There's no reason to purposefully alternate different loads in a modern pistol. Figure out what shoots well and stick with it. In my experience, M&Ps will feed and shoot almost anything well.