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9mm AR Build, Help Please

Strykervet

ain'T goT no how whaTchamacalliT
Full Member
Minuteman
  • Jun 5, 2011
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    Pierce County, WA
    So I've been building AR's for twenty years. I have all the shit to do it right, bed barrels, whatever.

    Never built a 9mm, considered a Glock lower because I had mags but it seemed more like a range toy than a real weapon. I got a Tavor and it uses Colt mags, I got a bunch of those now so I figure I'll entertain it again.

    I don't want to use a dedicated lower UNLESS I HAVE TO, in which case I'll shelve the idea. Buy once, cry once. But aren't there solid, semi-permanent or even permanent conversions for standard lowers that are reliable and function properly? Serious ones?

    My typical formula uses KAC shit, Geissele triggers, JP BCG and a Noveske bbl. for SBR's or a Krieger, etc. for longer ones. I get boring reliability and accuracy from this.

    So I'd like to use a JP BCG again here. And I know I want some kind of mag block that mounts in there solid and retains the AR mag release button if possible. Again, it's gotta be reliable, serious duty shit you can bet your life on. No range toys or gimmicky shit.

    It'll be an SBR, probably a 6"bbl. w/ASR flash hider and Omega 9k suppressor. I'd like to use a Maxim stock assy. unless there's a better/lighter one available for 9mm's that still allows use of the JP BCG. Is there an upper I should consider? Who makes high end 5" handguards?

    Ideas?

    Pictures?
     
    So I've been building AR's for twenty years. I have all the shit to do it right, bed barrels, whatever.

    Never built a 9mm, considered a Glock lower because I had mags but it seemed more like a range toy than a real weapon. I got a Tavor and it uses Colt mags, I got a bunch of those now so I figure I'll entertain it again.

    I don't want to use a dedicated lower UNLESS I HAVE TO, in which case I'll shelve the idea. Buy once, cry once. But aren't there solid, semi-permanent or even permanent conversions for standard lowers that are reliable and function properly? Serious ones?

    My typical formula uses KAC shit, Geissele triggers, JP BCG and a Noveske bbl. for SBR's or a Krieger, etc. for longer ones. I get boring reliability and accuracy from this.

    So I'd like to use a JP BCG again here. And I know I want some kind of mag block that mounts in there solid and retains the AR mag release button if possible. Again, it's gotta be reliable, serious duty shit you can bet your life on. No range toys or gimmicky shit.

    It'll be an SBR, probably a 6"bbl. w/ASR flash hider and Omega 9k suppressor. I'd like to use a Maxim stock assy. unless there's a better/lighter one available for 9mm's that still allows use of the JP BCG. Is there an upper I should consider? Who makes high end 5" handguards?

    Ideas?

    Pictures?

    In general the mag blocks fell out of favor as dedicated lowers simply increased the reliability of 9mm AR's with less tinkering. There are a few mag blocks out there that are pretty good but by and large the dedicated lower is going to be more reliable in the long run. Of those GLOCK pattern mags are preferred by a significant margin due to the availability, cost, aftermarket support and ease of loading (both bullets in and mag in gun). Whatever you end up going with I'd strongly recommend the bolt, spring, barrel and lower all be from 1 manufacturer to avoid compatibility issues. JP has silent captured springs for both the Maxim and Law stocks so you're good to use the JP bolt there. I like the MFT but pick whichever gets you going.

    Having said that, this is my suppressed SBR build that goes between suppressed configuration for night matches and other unsanctioned events to compensated for USPSA matches. Liked it so much I built a dedicated game gun twin. While I almost exclusively shoot games (matches), the reliability has been remarkable. We shot 4 people through a 250 round all steel match on the suppressed rig and it just kept on going. Between my 4 rifles I'm well over 150k rounds between practice, matches, loaning rifles out to other shooters.

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    ^^^^^Sounds like he has about 150 times the experience I do. I built mine because I wanted a range toy, and the AR Stoner parts were stupid cheap for my birthday special pricing. I started with a mag block and quickly moved to a Tennessee arms poly lower, that cost less than the mag block. I had to file it in few place to make it fit, then bend the ejector on it a little. Now its runs without a hitch. I use glock mags. I don't own glock's, yuck. :poop: :p:ROFLMAO:
     
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    Wasn't the original Colt SMG done with a block?

    So for a social weapon you'd say dedicated lower, period?

    In that case I'll just build 'em out as 5.56, 6.5, .300 --whatever. I have complete KAC lowers w/Geissele triggers and nice stocks that I'm finishing so not interested in doing up another. DONE with AR's after this too. Just have too many. So no block, no 9mm. And I don't want or need one bad enough to cut corners, so if there isn't a Colt style block you'd bet your life on then I have to pass.

    If I didn't have the Tavor in 9mm and the Kriss already I may consider it. If I do buy into another system though, it'll be because I sell the Kriss and adopt the BT.
     
    Or I suppose I could trade a new forged Noveske lower, not a chainsaw lower, for a GOOD dedicated 9mm lower that uses Colt mags... Preferably a JP but obviously open? Can swap complete or stripped and if the trade isn't even then I'll make it even.

    It'll be the only way I can do it. I'm sure someone has spare 9mm lowers like I have spare 5.56 lowers.
     
    Weren’t the original Colt 9mm blocks two pieces?
     
    Colt blocks were two pinned pieces. Anyone who repairs m16 receivers will be able to install your pieces if your receiver is close enough in actual dimensions.
    hahn block an easy quality solution
    I must believe not all lowers these days are dimensionally identically so ymmv
     
    Weren’t the original Colt 9mm blocks two pieces?
    The ones I've seen are - front piece holds the feed ramp and the rear piece holds the ejector.
    Hahn still has conversion blocks for Colt mags: https://hahn-precision.com/ar-15-mil-spec/
    I switched to ASC mags with the plastic followers because there was too much variance in the Metalform mags' followers (and even Colt followers) for reliable (mag to mag) last round bolt hold open (on a CMMG factory lower).

    Edit: SporterII posted same info while I was still typing.

    Bad pic of mine:

    Messaging1594068905890.jpg
     
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    I looked at the Colt block from Brownell's, you're supposed to drill and pin it in two places but in pictures on Wikipedia it shows the factory Colt SMG with 3 roll pins. The block and the receiver are drilled at the same time and it's not critical where the pins go.

    I have a drill press and am okay with drilling and pinning the lower for a permanent installation.

    I figure a Colt upper, JP BCG and a PDW style stock that allows use of the JP BCG. I figure the Geissele SSP trigger will work and I trust I can find a good 6" chromed CHF barrel for it along with a 5 or 5.5" FF tube? Suggestions? This sound like a doable and reliable setup? I've always had great luck with JP BCG's in AR's and I figure this would be no different?

    He mentions above to use like parts.... Does that mean I should use the Colt BCG instead for reliability over the JP?

    And Colt sells their SMG's with this block... It's how they make 'em. Is a dedicated lower STILL better? I'm selling my Noveske lower, I can put the proceeds toward a different one in that case.
     
    I have a mix of parts on mine sort of. The lower and upper are CMMG and originally 9mm, my lower takes colt mags. The upper was form 1d and I changed the barrel to the 4.5 inch. I can’t remember but I wanna say it was an old colt barrel but maybe not. It has been 8 or so years since I built it. I used the Troy Airborne stock that goes on an standard 4/6 position collapsable tube. The handguards aren’t super expensive but the work really well for what I do with it which is range blaster. The range gun
    6CC3CC53-DD20-43D9-A628-96A88076FA0B.jpeg
     
     
    Colt blocks were two pinned pieces. Anyone who repairs m16 receivers will be able to install your pieces if your receiver is close enough in actual dimensions.
    hahn block an easy quality solution
    I must believe not all lowers these days are dimensionally identically so ymmv

    I'd be doing it and it'd likely be a KAC or maybe LMT or Noveske.

    If it converts a lower into a defacto Colt SMG, it's GTG, right? Reliable and all?

    I have a mix of parts on mine sort of. The lower and upper are CMMG and originally 9mm, my lower takes colt mags. The upper was form 1d and I changed the barrel to the 4.5 inch. I can’t remember but I wanna say it was an old colt barrel but maybe not. It has been 8 or so years since I built it. I used the Troy Airborne stock that goes on an standard 4/6 position collapsable tube. The handguards aren’t super expensive but the work really well for what I do with it which is range blaster. The range gunView attachment 7367992

    That stock is the same size as the regular AR stock! The Maxim I have is a full two inches or more shorter and that's what I'm after on this one. A compact PDW style stock but if there's a lighter one that performs and functions like the Maxim, I'm all ears.

    It looks like I'm gonna have to cut down a URX4 to fit a Switchblock barrel since I can't find what I want. I may as well get two and cut the other one down to fit whatever size barrel I put on the 9mm. It being blowback, any size should work I figure. I'll look around first though.
     

    Would that be better than the Colt?
     
    I would phone and talk to Rudy at Macon Armory.

    He is "the man" when it comes to AR platform conversions.

    A few comments about Colt pattern conversions...

    Make sure your blowback 9MM bolt is compatible with your trigger groups hammer... lots of aftermarket hammers do not reset properly from the bolts ramp profile... mine only worked with a full USGI hammer profile. ( I had tried a Geissele Super TriCon, FWIW , didn't work properly ) If the very tip of your hammer is even slightly shorter or a different profile, the different ramp of the typical 9MM blowback bolt will not fully reset the trigger group.
    Many 9mm blowback bolts not have improved ramps or even a "added depth" to bottom of the bolt.
    The ALG Nic.Boron trigger works fine.

    Make sure to limit any excess bolt over travel into the buffer tube... the distance between the bolt face and the bolt catch should be limited to about 3/16"... any more than that and you risk breaking a bolt catch. ( Happens quite a bit )
    Buy a 9MM blowback extended buffer... you can "tune" to the 3/16" distance with a quarter ( or 2 ) in the bottom of the buffer tube as a spacer, under the recoil spring. ( Sounds silly, but it works )

    Speaking of buffers... 9MM blowbacks can be very hard on hammer pins, a heavy extended buffer is worth its weight in gold. I run a 7.5oz extended 9MM buffer. ... And a .308 Tubbs flatwire recoil spring ( Even JP recommends their 308 recoil spring for PCC's )
    So while a "normal" buffer weight and recoil spring will work... you'll find the percieved recoil

    I tried so many different combos ( recoil spring and buffer weight ) Sprinco Orange, red ..etc clear up to a 10oz buffer weight ( which caused serious muzzle dip ) and clear down the light weight trail...
    Ultimately , the 7.5oz buffer weight with the Tubbs 308 Flat wire recoil spring tamed its OEM percieved recoil impulse to a more acceptable level. Big difference compared to the Linda Blair ( Exorcist ) OEM setup... it is much more Winnie the Pooh now.

    That said... bullet setback in 9MM PCC's is a concern.. avoid Poly Coated bullet ammo, and Aluminum cased ammo. Those bullets set back routinely.
    Wide mouth HP's can give feeding fits ( SIG VCrown.. none of the various weights would feed reliably )
    A "good" crimp on the bullet is important.

    Colt pattern stick mags... ( Metalform ) .. be sure to clean the sticky packing inside the mags, and the follower. Brownells coated mags are Metalforms with a fancy coating applied inside and out. ( Wait for them to be on sale. )
    ASC's ... some 9MM Colt patterns run fine with them .. some don't , my mag block PCC prefers the Metalform mags.

    Keep you chamber clean... blowbacks can experience OOB discharges easily. So easy chambering is critical.

    I mention all this... so if you talk to Rudy, you can have some knowledge on what to ask about. He will help you choose parts

    All that said.... Make sure you express your desire for a 100% reliable PCC ( he can do that part ) , and remember ammo choice matters as part of that 100% equation.



    https://maconarmory.com/pages/about-us

    https://maconarmory.com/collections/all
     
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    The 9mm is 19 inches overall. Dropping to 17 doesn’t seem like a landslide and the portability would be same same in my opinion, but if you went shorter on barrel length you could start making big drops in overall length and not truly sacrifice 9mm performance for a PDW gun right?
     
    I looked at the Colt block from Brownell's, you're supposed to drill and pin it in two places but in pictures on Wikipedia it shows the factory Colt SMG with 3 roll pins. The block and the receiver are drilled at the same time and it's not critical where the pins go.

    I have a drill press and am okay with drilling and pinning the lower for a permanent installation.

    I figure a Colt upper, JP BCG and a PDW style stock that allows use of the JP BCG. I figure the Geissele SSP trigger will work and I trust I can find a good 6" chromed CHF barrel for it along with a 5 or 5.5" FF tube? Suggestions? This sound like a doable and reliable setup? I've always had great luck with JP BCG's in AR's and I figure this would be no different?

    He mentions above to use like parts.... Does that mean I should use the Colt BCG instead for reliability over the JP?

    And Colt sells their SMG's with this block... It's how they make 'em. Is a dedicated lower STILL better? I'm selling my Noveske lower, I can put the proceeds toward a different one in that case.
    You seem to be wanting to do a lot of work here. I paid $140 for the CMMG lower that I bought pre-hysterics, and it came with a 9mm bolt catch already installed (along with the feed ramp and ejector, obviously).

    I always wanted to try one of the Quarter Circle 10 lowers because they are more streamlined at the front of the magwell but I couldn't pay the entry fee.

    There's a few correctly-ramped 9mm BCGs out there but get one with a removeable weight that doesn't alter OAL of the bolt if you want to run a JP SCS or similar.
     
    Vet, good parts result in good assemblies. Should be good but I am just an opinion I have no control.
    as to the new age lower, There is more of these than I am used to. I hav had most versions of Colt 9mms and always running. Matches and lots of rounds flawless, every time.
    all I know.
     
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    I went with the Qc10 colt pattern lower. preferred the magwell fit but that's just me.
    This little guy eats and lrbho functions flawlessly

    Been running a cmmg ramped bolt with a Timney 3lb flat shoe with no issues for some years now. As far as buffer system, having tried all from spacer to dedicated 9mm buffer, and a variety of buffer springs. I have happily found my zen with the Blitzkrieg hydraulic buffer and a Tubb .308 flatwire spring, life is good.

    If I were to do it again in today's current market I think I'd give the cmmg rdb system a try vs db
     
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    They make 9mm magazines that are the same size as a 5.56 magazine. No need to run a mag block. There is also a mag block that uses Glock magazines. I have no idea how either run as I use Colt pattern magazines.
     
    Another vote for QC10. Although I went for a Glock lower since I have a couple Glock 9mm's. I went with their lower, bolt and 5.5" barrel and Seekins upper/handguard. It's more accurate than I could have ever imagined, and has run without problems since day one.

    Screenshot_20200706-211555.png
     
    I have a mag block in a stag lower using colt mags. Just like has been mentioned on the first post they will take a bit of tinkering to work 100%. I have to keep up cleaning every 2k rounds give or take.

    The upside is that I can run my mouse fart pistol USPSA loads or +P loads with no problem and I get to use the metal colt mags.
     
    They make 9mm magazines that are the same size as a 5.56 magazine. No need to run a mag block. There is also a mag block that uses Glock magazines. I have no idea how either run as I use Colt pattern magazines.
    The 9mm adaptors for Magpul gen 2 & 3 mags work very well. Just wish could find a way to run Colt mags with a CMMG RDB upper.

    OFG
     
    Here are two of my 9 mm AR's. Both good enough to qualify for advanced rating at the elite Rogers Shooting School close quarters carbine course. The school uses the Colt 9mm with blocks. The 16" Colt 6951 is a dedicated 9mm steel magazine receiver. The Wilson Combat AR9G(glock based) I assembled as desired.
    Using a 9mm SBR suppressed is shooting a 16" rifle.
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    The Stern Defense magwell insert works well, EXCEPT that the mag release on your receiver is what releases the insert. If your brain is programmed for the ar-15 platform this will be a problem for you, because you’ll hit that mag release and drop the mag well insert to the ground instead of just dropping your Glock mags. But it fits, and is adjustable for rock solid fit, and functions reliably with the uppers I’ve tried. You will definitely need the heaviest buffer you can find to slow the bolt down from the blowback operation.

     
    Shit, the more I learn about these the less desirable they seem.

    Maybe I should dial it down, use the one Mega SBR'd lower I have and just use the basic Colt parts. And a basic CAR buffer tube. If the Geissele triggers won't work then I can just use a stoned LMT AR trigger, I can get those down to 4.5lbs. for free. No need to really FF the barrel and I'm not looking to put a lot of money into this. Chances are it'll keep iron sights too.

    I know a shit ton about the standard AR but didn't know what I didn't know about these obviously. Thanks again. This'll help prevent waste of cash and mistakes.

    I think I can use this info to make a really nice 9mm SBR suitable for HD and farting around and I'm probably gonna go the Colt method from asshole to appetite while heeding the advice above about recoil and the geometry concern with the bolt and buffer assy.
     
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    I am not a fan of Magpul 556 mags, but a company named Mean makes inserts to convert them to 9mm, this has peaked my interest in building a 9mm upper for my SBR AR15, no mag adapter needed

     
    Shit, the more I learn about these the less desirable they seem.

    Maybe I should dial it down, use the one Mega SBR'd lower I have and just use the basic Colt parts. And a basic CAR buffer tube. If the Geissele triggers won't work then I can just use a stoned LMT AR trigger, I can get those down to 4.5lbs. for free. No need to really FF the barrel and I'm not looking to put a lot of money into this. Chances are it'll keep iron sights too.

    I know a shit ton about the standard AR but didn't know what I didn't know about these obviously. Thanks again. This'll help prevent waste of cash and mistakes.

    I think I can use this info to make a really nice 9mm SBR suitable for HD and farting around and I'm probably gonna go the Colt method from asshole to appetite while heeding the advice above about recoil and the geometry concern with the bolt and buffer assy.

    Pretty much. Putting 9mm into the AR platform is mostly compromise and cut corners. They are fun though. If you want reliable in an AR-15, 223 Wylde is your huckleberry. LOL
     
    I am not a fan of Magpul 556 mags, but a company named Mean makes inserts to convert them to 9mm, this has peaked my interest in building a 9mm upper for my SBR AR15, no mag adapter needed

    9mm inserts for Magpul mags work very well. Never had a FTF or other problem. It is good to run a CMMG rdb upper on a 5.56 SBR lower.


    OFG
     
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    I put together 2 9mm AR, 1 Colt mag and 1 Glock mag. Both 4" BBL and run well with no issues but I would recommend going Glock dedicated lower. 1 for glock mags and 2 for overall costs. I had a little concern about gas running suppressed so your concerns about gas holes may vary.

    The Colt was first and costs were unnecessarily higher. I went with a Hahn top insert. This alone cost more than my glock lower that came with a magazine release and bolt catch. On the Colt I went with a 8.5 oz buffer from heavy buffers.com (9mm-Q Buffer + Wolff XP Spring). This works real well but the weight of the pistol is noticeable. My basic buffer detent was bending forward later updated it with Leitner Wise thick steel one. I used a Colt brand 9mm upper as it had no gas tube or a FA. As for the mags it is fine with C Products mags. I did sand all of the followers sides prior to shooting them as it was suggested. Colt mag prices are much higher.

    For the unplanned Glock, a LGS had a their branded name on Glock lower and I went for it. This experiment I used the JP 9mm silent spring and happy with its weight savings and performance. I made the Glock a side charger with a Gibbs arms upper. This has a gas tube but its a threaded hole. I found a flat allen screw that plugged it up perfect. The fit and finish is great and hind sight I wished I had bought their matching lower.

    (No I don't run the optics this way. Just a pic I took after it was together and messed around with a spare)

    Also Lesson learned 3 lug sucks.

    cUDsqNE.jpg
     
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    I built mine using the Colt system, Metalform stick mags. Whichever barrel i've selected (multiple uppers), I've sent it to Rudy (Macon Armory) for his feed cone enhancement for improved feeding reliability. Some 9mm barrels are atrocious with their feed cone, e.g. straight beveled chamfer instead of a gentle radius. I use the Hahn dedicated block in a USGI mil-spec lower, that thing is rock solid, absolutely, pricey though, also provides last round bolt hold open. Gotta remember to use a 9mm-specific mag catch (RRA), the genuine Norgon has the requisite extra bite depth on the mag catch tooth. Trigger reset with non-USGI mil-spec triggers is an issue if you're not careful with bolt selection. You want the bolt with the extra speed bump on the bottom (pic below, front sample), that helps with trigger reset with non-USGI-style triggers, Geissele for instance, still some variance depending on which make/model. Otherwise you'll discover inconsistent trigger reset, if at all. I use the KNS Gen G pins, supposedly a little harder. I use the VLTOR A5 buffers in a standard M4 carbine buffer tube. the A5 buffer has the extra length that would otherwise be used with a spacer, or 9mm-specific extra-long buffer, while still retaining the reciprocating internal weights to minimize bolt bounce. Select the buffer weight for last round bolt hold open. check to minimize the distance between the bolt catch and the bolt face with the bolt fully retracted, use shims (e.g. quarters) to minimize. The heavy-ass bolt rebounding, if allowed a running start at the raised bolt catch, will snap it off, not the fault of the bolt catch, so you want to minimize that. When you choose your barrel, pay attention to the muzzle thread pattern used, e.g. 1/2-36, it varies by mfr, make sure it matches your chosen muzzle device, and make sure your MD has a big enough hole for 9mm bullets to pass through. If you're using the iconic gas deflector with the truncated ejection port door, then your upper doesn't need a brass deflector, so if you're choosy with your build, get a stripped upper that doesn't have a brass deflector, and doesn't have a forward assist, i.e. a specific 9mm AR upper. Doesn't need to have a gas tube hole either.

    JMHO, YMMV.

    SljYCbV.jpg
     
    Well, I have some more parts now. Sort of. And I'm ready to pull the trigger on the rest.

    I got a Colt upper and a Colt 1 piece block I need to pin in place. I got an extended bho device. I got a JP bolt but it was the older one and had to send it back, not the droid I was looking for.

    So I'm considering JP bolt/barrel/buffer. Not really feeling the 10.5"bbl. and 1/2-36 threads though. Is there another barrel that will function reliably with the JP buffer and bolt? Or should I just suck it up and go with the JP barrel because it's by far the best option?

    I'd like to be able to consider a 5"bbl. though, I figured on maybe mounting a suppressor under a 9" handguard. With a 10.5" I'll stick with an Omega 9k and an ASR mount, probably with a 9" URX4 handguard.

    Ideas? Suggestions?

    Also, what's up with the "short stroke" buffer assy.? Do I need that, should I get that? Will LRBHO work if I use the JP 3rd. gen bolt with it? Is the 11oz, buffer sufficient? The basic one?

    I want a svelt, reliable and fairly accurate (within reason and range) 9mm carbine, good with +P+, good with 158gr. subs. I'd like to be able to use it for HD so reliability is key.
     
    Screw it. I got the JP parts, 3rd gen bolt assy., "enhanced" standard buffer assy. (not the short stroke) and 10.5"bbl. Should be a reliable and accurate setup.

    That'll be 11.2oz. for the buffer, supposedly sufficient for suppressor and/or +P+ use and LRBHO works with no bolt bounce. We'll see. The claim is the standard buffer assy. is more reliable so I went with it.

    I guess now I just gotta get another ASR mount and wait for all this stuff to get here and I can put it together.

    I'm figuring it'd be best to get it all assembled and only pin the 1 piece Colt block once everything is working properly?
     
    Just put cobbled together this 4.5" 9mm Rock River Arms with upgrades. Single point sling and Law Tactical folding adapter to be installed.
    Off to the range tomorrow.
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