Thread: pistol caliber ARs

howdy

i'm thinking about building a pistol caliber AR, looking for some info from those of you who happen to have some advanced knowledge

my background is in 223/556 ARs- i've been building, armoring, and shooting this platform for over a decade, including professionally at times.. my working knowledge is very strong. but take my outside that realm, and i know basically nothing.

i DO know that pistol caliber ARs are blowback, and at least the 9mm models require either a dedicated hammer or a ramped carrier.. that thats about it.

so.. some questions:

-WHY do 9mm ARs require one of these mods?
-do other pistol calibers require those mods?
-do 9mms use dedicated bolts, or does the standard 556 bolt work?
-what's availability of internal parts like for other pistol calibers?
-why do 9mm uppers have modified port doors and big, hideous brass deflectors?
-do other pistol calibers require this mod?
-is the upper modded in other ways, or will a standard forged AR upper work?
-can 9mm conversions be made to accept glock mags?

thats all i can think of off the top of my head, for now

thanks

I have a gas op 10mm but mags are finicky and the standard carrier needs a little narrowing on the underside to feed

Why not stay with tried and true and common? With a pistol round your going to pay about the same for ammo, get less capacity, and less velocity and energy. It looks like a high cost mod with no return. What am I missing?

Originally Posted by SheepDog223

Why not stay with tried and true and common? With a pistol round your going to pay about the same for ammo, get less capacity, and less velocity and energy. It looks like a high cost mod with no return. What am I missing?

fun

Originally Posted by SheepDog223

Why not stay with tried and true and common? With a pistol round your going to pay about the same for ammo, get less capacity, and less velocity and energy. It looks like a high cost mod with no return. What am I missing?

Suppressed 5.56 is still loud. Suppressed 9mm can be stupid quiet.

this thread is NOT to debate the merits, or lack of, of pistol caliber ARs. straight up.

Originally Posted by bkb0000

this thread is NOT to debate the merits, or lack of, of pistol caliber ARs. straight up.

Sorry. I have always wondered why the AR platform was used for pistol cal's and thought this was the time and place to get that question answered. Didn't know I started a debate. Sorry I may have taken to much liberty in asking a random question. Straight up.

Originally Posted by SheepDog223

Sorry. I have always wondered why the AR platform was used for pistol cal's and thought this was the time and place to get that question answered. Didn't know I started a debate. Sorry I may have taken to much liberty in asking a random question. Straight up.

not trying to be a dick- if your post was purely question and no imposition, then i apologize. i just want to keep this one on topic, and not devolve into 4 pages of debate and have none of my questions get answered. nah mean?

but to answer the question, i DO actually have a semi-logical reason for being interested in pistol cal ARs.... blowback. when you have no gas-operation, you have no barrel length consideration- you can go a LOT shorter than convention 5.56/DI guns without the inherent reliability problems associated with VSBR ARs.

it'd also be cool to have a truck gun that will accept glock mags, but i don't know if there are 9mm setups that take glock mags

Ok now to answer questions, rather than spout mindless drivel.

I built a cool little 9mm AR, so my limited knowledge ends there. I use a standard upper. Those fugly shell deflectors are more for lefties. The bolt is dedicated 9mm/10mm etc. Mine is modified to work with standard AR hammers. I run a spikes Tactical magwell for colt style stick mags. Cheap C products work great for me. Uzi mags are easily modified with a dremel. I will try some this month. I've seen some dedicated lowers (olympic?)that run Glock mags but good luck finding one. Another consideration is the buffer. Either a longer heavier 9mm buffer is used or a heavier 556 buffer with spacer. I run a spikes 9mm buffer. Hope that helps. Glad to help answer questions, if I don't know the answer Ill tell you.

Not really sure if the 9 setup is much different from a .45, but setup wise, the upper my Olympic arms .45acp came in is just a regular upper, but has a dedicated bcg, brass deflector, ejection door are all spec to a regular ar15, I know the guy from custom firearm stands made a 9mm AR and it was as simple as getting the upper and a regular ar15 and slapping them together. The only thing I dislike about pistol AR is the buffertube, its fugly and makes it look like a tennis raquet.

Originally Posted by spider

The only thing I dislike about pistol AR is the buffertube, its fugly and makes it look like a tennis raquet.

this won't be a pistol.. just pistol caliber.

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thanks for answers so far... so the gigantic brass deflector doesn't serve any functional purpose at all? it's JUST to keep brass out of the face of lefties? and the half port door- is that just to accommodate the gigantic brass deflector?

Originally Posted by bkb0000

thanks for answers so far... so the gigantic brass deflector doesn't serve any functional purpose at all? it's JUST to keep brass out of the face of lefties? and the half port door- is that just to accommodate the gigantic brass deflector?

I run one on my .45 upper. It helps tremendously to cut down on the amount of gas blowback. And it's nice to have the brass thrown forward rather than backward.

Before, if I ran a bunch of rounds through, there'd be enough nasty gas coming back that my eyes would tear up. Even more so when running suppressed.

I am running an Oly Arms 9mm conversion on my M16 lower. I have had it for over 15 years and probably have over 8k rnds through it. It uses a standard upper that is modified to have the ejector housed in the upper receiver and uses a mag well adapter that uses sten mags. I believe the newer ones use a new mag with no adapter. It's nice to be able to just slap the 9mm upper on without having to change anything else.

Originally Posted by bmgm37

I am running an Oly Arms 9mm conversion on my M16 lower. I have had it for over 15 years and probably have over 8k rnds through it. It uses a standard upper that is modified to have the ejector housed in the upper receiver and uses a mag well adapter that uses sten mags. I believe the newer ones use a new mag with no adapter. It's nice to be able to just slap the 9mm upper on without having to change anything else.

in relation to this, another general question: why do in-bolt ejectors not work? is the casing just too short to ensure flinging clear before it falls off the extractor?

Originally Posted by SheepDog223

Why not stay with tried and true and common? With a pistol round your going to pay about the same for ammo, get less capacity, and less velocity and energy. It looks like a high cost mod with no return. What am I missing?

I get my subsonic 9mm (Winchester Super X unleaded 147gr) at the gun shows for around $12 for 50, do you have line on cheaper .223 than that?

Most AR(.223) mags are 30 rounds, most 9mm AR mags are 32 or 33 rounds.


I'll agree on the less velocity and energy issue (unless) you are talking about subsonic rounds. I haven't really looked into subsonic .223 or 5.56 ammo (mostly because a really heavy .22lr bullet comes to mind) but I'd have to suspect that it packs quite a bit less "punch" than 147 gr 9mm.

Originally Posted by bkb0000

in relation to this, another general question: why do in-bolt ejectors not work? is the casing just too short to ensure flinging clear before it falls off the extractor?

The case is too short. In a rifle round you are extracting for a good distance before throwing the round. If the round ejected itself off the bolt face it would likely stovepipe every time. There are two basic platform types available, Colt and Olympic. Colt uses a drop in or magwell converter with the ejector attached to it. Olympic has a spring wire ejector that is put through the upper receiver. Colt style is used by Colt, Yankee and Rock River. That big *** deflector is because due to the timing of the shorter case the standard deflector won't deflect sh1t. Feel free to PM for further details and pricing

Originally Posted by NoAim

Before, if I ran a bunch of rounds through, there'd be enough nasty gas coming back that my eyes would tear up. Even more so when running suppressed.

is this as a righty, or lefty?

Originally Posted by nubus

The case is too short. In a rifle round you are extracting for a good distance before throwing the round. If the round ejected itself off the bolt face it would likely stovepipe every time. There are two basic platform types available, Colt and Olympic. Colt uses a drop in or magwell converter with the ejector attached to it. Olympic has a spring wire ejector that is put through the upper receiver. Colt style is used by Colt, Yankee and Rock River. That big *** deflector is because due to the timing of the shorter case the standard deflector won't deflect sh1t. Feel free to PM for further details and pricing

i imagine there's really no way to go "drop in" upper on a lower, since the mags are totally different- is there any benefit to the oly style over the magwell ejector, factoring the necessity of a conversion?

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and i thought i posted this earlier, but i must have farted or something: does Colt make a non-FA (and therefor available to ME) factory 9mm SBR? all i can find is A2-uppered 16" guns... i don't necessarily mind having to chop the barrel, but the A2 upper is just going too far.

Initial cost is the only advantage IMO. The mags are cheaper for the Colt style once you have it. The magwell drop in is around $150-180. And what difference does the bolt make? FA or not it won't rock and roll without the proper registered lower. I'm not sure about Colt but Rock River does make SBR length barrels. I would buy the lower of your choice and SBR it multiple cal and just buy the upper you want. A whole SBR from Colt or RRA will be spendy.

i'm seeing the Colts for around $1050, which isn't bad at all for a complete colt carbine- but it's a configuration i have no interest in. once i swap uppers, chop and thread the barrel, add a buis, swap furniture, and add an optic, it'll be upward of $2000. screw that.

Originally Posted by bkb0000

is this as a righty, or lefty?

I'm a right handed shooter.