I have a new M&P 9 , is using +P ammo a bad idea ?

It's fine.

I just bought a Shield 9 also and called S&W to ask about +P.

They said you could shoot +P "all day long"

My M&P Shield 9 can shoot +P ammo, but I don't shoot it all the time, because, as it states in the manual, +P rounds can shorten the service life of some of its components. I'm guessing that your M&P 9 manual has a similar statement.

I use Hornady Critical Duty 135g +P as my SD ammo in my Shield. I chose it after extensive testing of several kinds of SD rounds, and it was the only one that did not have a single FTE or FTF. Initially, the Honadys were not as accurate as some of the other brands, (the Hornadys all wanted to go left), so it's taken some extra practice to get them on target, but they're OK now.

I've put around 200 +P rounds through my Shield (out of 3800 total rounds), and it shows no unusual signs of wear. So go ahead and shoot 'em, just don't overdo it.

Enjoy your new M&P!

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What, me worry?

I'd carry them with no hesitation, but mostly practice with standard pressure ball ammo...to save both money and wear and tear on the pistol.

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No good deed goes unpunished.

So somebody explain WHY +P to me. I don't get it, unless you have enough $$$ to practice with it a lot to be sure the pistol works, and you're accurate with follow up shots with it. Good normal pressure 9mm does the job 99 times out of 100.

If you handload, the difference between +P and standard is maybe $0.001 more powder. That's 1/10 of a cent.
In 9mm, it is easy to make minor power without +P.

If you want certain factory loaded defense bullets, some of them only come in +P, so you get it automatically.

In my experience, loading regular 9mm 124gr for practice and shooting +P 124gr HP for defense gets the POI so close that you can effectively practice without shooting the expensive +P defense loads all the time.

SAAMI spec for regular 9mm is 35,000PSI, while +P 9mm is 38,500 PSI, so in a modern quality 9mm pistol, +P is really no big deal.

Some people (not I) are loading and shooting MAJOR POWER 9mm in M&P 9mm pistols in USPSA OPEN Division, which is completely off the top of the SAAMI pressure chart for 9mm.

So yeah, IMHO, you can shoot +P all day, every day, in an M&P and maybe it will wear out sooner, like at 80,000 rounds instead of 100,000.

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Science plus Art

When they say "it shortens service life" they mean long term. Instead of getting a 100k rounds it may be 95k or 90k. If you rarely shoot it it makes no difference

Me velocity, more energy.

115 gr has about 1300fps and about 400 ft-lbs of energy. While the +P has around 1350 - 1400 fps and 450 ft-lbs. +P+ has over 500 ft-lbs. Of course barrel length makes a difference.

The 9+P is actually 9NATO

+p is fine, that's what I keep in mine. (corbon dpx), 1250 fps, 399 ft. lbs.

I just like the corbon +p cartridge. I've shot hundreds of rounds before making that decision. Federal HST, Hornady, Gold Dot, all in normal pressures. I just like the feel and performance of the Corbon and I shoot it well, it's a proven round, good barrier penetration, etc. Never had a malfunction with this round in any of my guns (1911, 357).

Personal preference. I'll run a mag through every trip to the range or every other trip.

edit: I especially like the 185 gr. +p DPX in my 1911, Talk about sweet shooting.

Use it, love it, doesn't significantly increase felt recoil for me, never worried about wear and tear. I shot 9mm NATO for years in Berettas and Sigs, thousands of rounds, no issues. As someone else here said, it might decrease service life from 100,000 to 80,000 rounds. DANG! Means I'll just have to get another!

personally, my backup ammo is american gunner 124 gr xtp +P. I say backup because I can't find any of the big 4 anywhere. I find this ammo easily at Cabelas most of the time and since it is for personal defense only after I make sure a sample from each box chambers properly, it tends to last well because it is meant to defend not target shoot. Even though it is not rated as highly as speer gold dot 124 gr +p or Federal HST 124 gr, it is pretty much available.

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Regards from THE Old Fart