Will My AR-9 Pistol Handle +P+ ?

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weblance

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I have a CMMG MK9 pistol. It has an 8.5" barrel. My local dealer has Federal 115 GR +P+ JHP (9BPLE). It has a rated velocity of 1,300 ft/s. I'm not planning to shoot thousands of rounds of this ammo, but possibly 500 throughout the life of this weapon. I would buy a couple hundred rounds, test them for function, then use it for home defense. Every once in a while, I would fire the whole magazine(32 rounds).

I understand the bolt catch may be the weak link in AR-9s. What do you think...?
 
I'm just going to go out on a limb and say you might want to ask the rifle guys as well. I understand it's an AR pistol with an 8.5" barrel BUT the are probably some rifle guys that know the AR platform inside and out that might be able to give you some answers? Even with the gun being classified as a pistol and in a pistol caliber.
 
With the limited amount you are discussing, I would have no fear. I honestly don't believe a steady diet of that ammo would harm anything. The 5.56 round developes much more pressure, and you aren't compromising much bolt lug locking surface with 9mm. The locked bolt of an AR will handle it much better than the breach lock system of a pistol.
 
You should be aware that +P+ ammo has no standard pressure. SAAMI standards include standard and +P ammo and have pressure standards for them. +P+ loads might have less, the same or more pressure but that rating is mostly a sales gimmick. +P+ loads are typically operating at pressures below the maximum +P pressure according to the articles I have seen.
 
Uzi's were designed to handle hot 9mm ammo. I mention Uzi because it is blowback operated like your ar15 9mm carbine. The UZI has a big and heavy bolt to remain in battery and handle the higher pressures. My colt 6951 9mm ar has a heavy bolt too, but not as beefy as my IMI model b Uzi. Without a delay mechanism like a browning short recoil locking design like many modern semi auto pistols, direct blowback design require heavier bolts to prevent out of battery ignitions from hotter ammo. I suggest you ask cmmg first.
 
My MK9 IS a blowback, as are all(?)AR-9s. I'm simply curious about this load, as its significantly cheaper than all the good Self Defense rounds, and seems to offer more velocity. I'm also trying for ultimate reliability. After a bit of polishing on the feed ramp and underside of the bolt, and removing all bolt drag from the magazine feed lips, this gun has chambered and fired perfectly many different types, and brands of ammo. I would like to try everything I can find, especially every different hollow point brand.
 
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The first thing I would do is weigh your buffer. Most factory built ar9's use about a 6oz buffer. Swap it out with one that's 9oz or more then check for case eject pattern.
 
There is no industry standard for +P+, it is whatever the ammo company thinks the guns will stand. That said, the 9BPLE has been around for a long time and has a good reputation. While it does not have the latest and greatest in the Bullet Of The Month Club, it is fast, accurate, and reliable. Also available by the 50 instead of the 20 shot BOTM ammo that won't even fill your magazine.
I use the standard pressure 9BP, myself.

I do not know how it will behave in a blowback AR "pistol".
 
I emailed CMMG and they told me the 9BPLE +P+ load is fine to shoot in my MK9. They also stated that the +P+ load may wear parts faster, and I could use a heavier buffer if the felt recoil was objectionable, but not necessary.
 
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