9mm sbr on ar platform

[Icky The Great]

Does anyone have any experience with ar platform 9mms?
I am thinking of doing an SBR and suppressing it.
Thoughts?

 

[Telekinesis]

I don't have any experience with 9mm SBRs beyond one being on my list of eventual projects, but I think it'd be a fun toy. You should be able to get a nice compact package with a 5" barrel and suppressor. I think that would be about a perfect length if you ran the hand guard over the suppressor so you could have your hand out front.

Not sure how much experience you have with suppressed ARs, but as a shooter you still hear a lot of spring noise when you fire it. I never thought of my .300 Blk suppressed SBR as quiet until the first time I stepped back and let a friend put a few rounds through it. It sounded like a completely different gun (and it is in fact "giggle quiet" )

FWIW I'd try to register a standard AR lower and use a block that goes into the magwell. That way you can still use the registered lower for other standard AR calibers in the future. On the other hand if you already have one or two AR SBRs, there are some pretty cool looking dedicated 9mm lowers.

 

[Icky The Great]

TK, I was thinking of doing the fore end over the suppressor but I definitely want 10" or 11" barrel. I fully intend to make the gun convertible to 556. I am more so wondering about functionality. I heard bad things from the old Colt 9mm carbines and was wondering if the problems followed along the chassis being retro fitted or just poor design issues. Also the 9mm as of late are typically blow back operation so you will not get so much spring noise. My Uzi has a lot of spring noise when its fired shouldered and I am wearing cans but if I put in plugs I do not hear it at all.

 

[jmorris]

When I built one. I wanted a suppressed 9mm that was no longer than a 16" carbine with the suppressor but didn't want to pay for two stamps for the same rifle. So I made the suppressor part of the barrel and it is 16.125 with the end cap removed.

 

[jmorris]

It's pretty quite hard to tell sound by a video but you can hear the wind and impacts on the steel plate 100 yds away makes more noise than the rifle. You can even hear the tree branches getting hit when he misses.

 

[Ironman]

Suppressed 9mm SBR
http://youtu.be/9ay8vpdAysQ?t=6m9s

 

[eldon519]

I've got a 9mm AR-15, a recent-manufacture Colt. It has run well with no issues so far. I don't even really clean it much, just add a little oil to the bolt from time to time. They get filthy inside in about 2 shots, so not much point trying to keep it spotless. What kind of bad things have you heard about them? I'm not positive, but I think the old Colts did not have ramped bolts which made them more prone to beating up the hammer and egging the pin holes. They do have a surprising amount of recoil, actually probably a bit more than a 5.56 (I've got two nearly identical Colts, one 9mm and one 5.56).

I thought about doing the SBR/suppressor thing, and was really interested in getting one of the TROS 3-lug barrels and sticking an AAC Evolution on it (great value and comes available with 3-lug mount). Regarding the barrel length, as mentioned, a shorter barrel length is a smart idea unless you reload your own ammo. If you go with a 10" or 11" barrel, you're gonna have to download it to keep it subsonic or be dedicated to the pricey 158-gr stuff (even that may go supersonic in a 10" barrel, not sure). If you go with a 5" barrel like TROS makes, you should be able to keep factory 147 and 158 ammo subsonic.

Anyway, that was the fruit of my research labor. I recently shot a suppressed gun for the first time though and figured out that it just wasn't for me, so I abandoned the idea.

 

[Icky The Great]

Eldon519, Thanks for the input. As far as the older Colt Carbines go I had talked with some FBI guys who said they did not reliably feed, tend to stove pipe, and didn't always cycle properly. 2 of them surmised it was due to fouling in the chamber. I tend to disagree for the reason you mentioned that they dirty in two shots. I am tending to think it was more a mechanical issue. Either with the adapter or mechanism, bolt or feed ramp. I never had a chance to play with them so I do not know first hand. Thus me asking about them.
JMorris, that thing is sweet! I however would like a separate suppressor so as I can swap it onto other firearms. And that way I could convert the SBR into a 223 and put my can on it legally and easily. If I had machining prowess I would certainly be making my own as you did.
Ironman, I checked those out previously. It was an idea and those help move it along.

 

[AverajeJo]

Would the TAVOR work for you in 9mm? It is shorter than most SBR and it has 16" barrel. That could be sweet.

 

[Arizona_Mike]

I built one. Had some disconnector issues, and some magazine issues that I finally solved (I discussed them in detail here and on AR15.com). You want a mag that works well with your adapter block or dedicated lower. I had to go with Metalforms for my Hawn adapter block (did not want another stamp), but not until after I bought a bunch of C Products mags which are very nice but they tell me are designed to feed in dedicated lowers. You can never do enough reading and research. There are ramped and unramped carriers and they work with different hammer types.

Looking to sell the barely used C Product mags . . .

One thing to keep in mind is bolt velocity. Historically proven blowback firearms have about 4m/s slide velocity. 9mm AR15s are designed to run much faster than this and are hard on the brass and run dirty. Adding a suppressor is going to make it into a soot factory.

I recently posted this on the MechTech Forum: http://mechtechsys.com/forum/viewtopic.php?f=3&t=12556

The most successful blowback designs (open or closed bolt) in history tend to have bolt/slide velocities of about 4 m/s (12 ft/s). 9mm AR15 is much faster than this (extra heavy buffers can get this down into the 6 m/s range and this is why 9mm ARs are so filthy). Ever notice how the CCU is remarkably clean. It's unconventional high spring pre-tension design helps a bit but nothing delays opening of the chamber like weight.

If you look at the "right" weight for a closed bolt blowback (reciprocating mass to achieve 4 m/s) from this excellent article: http://www.orions-hammer.com/blowback/ the CCU's bolt/bolt carrier is bit heavy but not total overkill compared to what is needed for .45ACP (2.3 lb) or 10mm (2.8 lb)--not to mention .45 Super, but is overkill for 9mm (1.7 lb). You actually see that it is a pretty good design for one-size-fits-all.

Either enjoy your very clean-firing, very low recoil CCU or start skeletonizing the bolt carrier (and kiss any warranty goodbye), but you should do your research first. Start by understanding the blowback design article I linked to above.

Short of going Tungsten, this is the best 9mm buffer you can buy: http://www.spikestactical.com/st9x-9mm-heavy-buffer-p-1187.html
The extra weight will get the bolt velocities in the 6m/s range (unsuppressed) and the extra length keeps the BCG from going too far back. If your lower or block has a LRHO feature, these are farther forward in the 9mm than 5.56mm and the BCG gets a running start at the slide stop. Some 9mm AR shooters break a lot of slide stops. By running the longer buffer, this is prevented.

Given how well my Mechtechs and my Roni SBRs run, if I had to do it over, I'm not sure I would.

Mike

 

[Icky The Great]

AverajeJo, I do like Tavors but that's not what I am going for on this build. I though a bullpup would be cool but I want an AR platform as I am building the whole thing from lower to upper.
Arizona_Mike, that's what I am looking for. I am not worried about cyclic rate so much as performance. I was reading up on the internal mechanisms of blow back operated sub guns but most info I found sketchy as it all seemed so opinionated one way or another. I will check those links out soon enough. At this point I probably write the manual to it before I ever get one pin in the frame.
jmorris, Did you machine those baffles yourself? I am wondering if they were reversed what the difference would be between them? As far as my idea of a suppressor, I am thinking along the lines of the DeLysle Carbine. In so much as using a helical baffle but basically a monolithic core.

So to clarify, I intend to build an AR capable of converting from 9mm to 5.56mm with little more than a tool or two. Having said that, I intend to have the uppers as SBRs, though not limited to this idea. The 9mm will be suppressed and I would like the barrel and can to be about 16"-17". Its a bit of a dream gun but I at least intend to start with some sort of plan in mind. I may make the can itself if I find access and guidance on a lathe or CNC machine. Haven't done much with that tech in many years so I am certain a lot has changed, at least as far as the programming goes. Do not bother looking for updates as I fully expect this to be many many months in the making. To much other crap to do now so any progress will be at the moment its available. Thanks for the help.
Hope people keep posting tech here. I will need it as I progress

 

[Arizona_Mike]

The one place my 9mm AR shines is accuracy. My ADCO 7" barrel shoots one ragged hole at 50yds.

Mike

 

[jmorris]

jmorris, Did you machine those baffles yourself? I am wondering if they were reversed what the difference would be between them?

Yes but I never fired it with them backwards but would suspect it would not be as efficient.

This is a different can but you can see the face and mouse holes of the K baffle better.

 

[Wisco]

I have a relatively new CMMG 9mm.

It's been 100% reliable out of the box with the mags that came with it, as well as Metalforms.

Once I can efile a Form 4, I'm getting a can for it.

 

[wally]

You want a mag that works well with your adapter block or dedicated lower. I had to go with Metalforms for my Hawn adapter block (did not want another stamp), but not until after I bought a bunch of C Products mags which are very nice but they tell me are designed to feed in dedicated lowers.

Funny I have both the top loading and bottom loading Hahn blocks and use the C-products / AR Stoner magazines. I will say that most of the mags did not work 100% out of the wrapper giving bolt over base (nose up jams) when feeding from the left side during the first 10 shots of a 30 round loading. After some internal finish has worn off they are working great now.

IMHO for suppressed you want a 5" or 7" barrel to help keep things subsonic.

On my 5" build I used the SIG arm brace while waiting for the SBR stamp as I already had a 9mm suppressor.

5" with fake suppressor & SB-15

7" SBR

My wife and I have a blast with these on a dueling tree. Here is the 5" with suppressor in its "final" configuration:

 

[dprice3844444]

my basic rule upon acquiring an ar platform,is to strip the bolt carrier group and check the extractor for an upgrade kit,if none,i install one.eliminates 1 problem before it occurs.if ftf issues occur,extraction is covered.

 

[gunsablazin]

If you get a 9mm AR take a good look at the CMMG guns. I have one, although I have not gone the SBR route yet, it is very fun AR just as it is. It is reliable, and plenty accurate, and cheap to shoot as well. It has become my favorite range toy.

 

[Arizona_Mike]

Interesting. My Hahn bottom loader loves Metalforms but my C-Products were jamming every 2nd round from the left side of the mag (every 4th overall). Never from the right.

Mike

 

[HRnightmare]

I have one with a 8.5" barrel. I shoot it suppressed and unsuppressed. It is one of my favorite guns.

A 9mm out of a barrel that length is no puny little round. I can nail targets at 50+ rds with pretty good force. Still very lethal.

 

[HRnightmare]

If you get a 9mm AR take a good look at the CMMG guns. I have one, although I have not gone the SBR route yet, it is very fun AR just as it is. It is reliable, and plenty accurate, and cheap to shoot as well. It has become my favorite range toy.


Mine is a CMMG 9mm dedicated lower - I read all the problems with the magwell blocks so I went dedicated. I have shot about 500 rds thru it, suppressed, unsuppressed, steel cased, brass, HPs, FMJ, subsonic, supersonic NOT a signle issue.

My upper is a 9mm RRA pistol upper. Ill upload pics later.

 

[jmorris]

I used the mag block model1sales has, it even works 100% with the $12 promags but the Colt mags are much more durable.

 

[wally]

Interesting. My Hahn bottom loader loves Metalforms but my C-Products were jamming every 2nd round from the left side of the mag (every 4th overall). Never from the right.

That pretty much matches my experience with most my the C-Products / AR Stoner mags when they were new, some were much worse than others but it was always a left side round (or odd numbered shot starting with a 30 round load) although the first one always fed from bolt release or charging handle. The steel cased ammo I was shooting usually has a bit more friction in mags, so its possible a few more would have been OK initially with brass cased ammo. Did you have black or orange followers? None of my black followers activated the BHO until I filed them to come up high enough in the empty mag, but my recollection was most of the ones that fed 100% from the git-go had the black followers

Maybe yours just needs some more usage, maybe using steel cased ammo a few times is the key to wearing off the excess finish inside, but once they develop shinny "lines" inside the top couple of inches of the body they've worked 100% for me. We run them hard on the dueling tree, typically shoot 6-10 mags (180-300 rounds) thru each gun during an outing. I think I have 28 mags total for the two 9mm SBR and 9mm AR carbine.

The 3 ProMags I tried worked well initially after I trimmed off the molding flash that interfered with seating them. But the plastic suffered creep and I started finding loose rounds in the range bag and short loads in the magazines. My mags for my favorite guns tend to sit loaded so as to be ready to go when a shooting opportunity pops up, maybe the ProMags would be OK if you just loaded them and shot them soon after.



I have a ~$10 ProMag loading tool that really helps, but even with it the last two rounds are just too much trouble to generally bother with. Can't believe I've just recommended something from ProMag My buddy took the basic design idea and made one for my 7.62x39 AR mags on his 3D printer using PLA polymer, works great! They also sell one for 5.56 AR mags and it also works well, although 5.56 AR mags generally thumb load without a lot of pain.

 

[Arizona_Mike]

The problem is every 4th 9mm round gets converted into a .380. If one slips by inspection and gets reloaded, the case gets turned into a belted magnum. I'm not going to be "breaking in" my C-Product mags with my gun or my face anywhere near anyone else's gun.

I already have 7 Metalforms that are working great. I'd much rather sell the C-Product mags in like-new condition to someone whose gun likes them. They are the latest incarnation of the orange follower (the rust red ones) that are supposed to be the best made.

Mike

 

[eldon519]

Yeah, Metalform is where it's at. That's what Colts ship with from the factory.

 

[Arizona_Mike]

The one thing I don't like about the Metalforms is how delicate the LRHO tab is (clearly an afterthought in the design). I had one arrive broken off from Brownells (of course they made it good). They are expensive but Brownells' FFL discount take a bit of the bite out of the price vs. other mags.

Mike