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SBRing a RRA 9mm Carbine

Discussion in 'NFA Firearms and Accessories' started by minutemen1776, Aug 1, 2012.

  1. minutemen1776

    minutemen1776 Well-Known Member

    I've been looking at Rock River 9mm AR carbines lately. I love the AR platform and shoot a lot of 9mm handguns, so I'm thinking this might be a good buy for me. One added draw (I think) would be that such a carbine would be a good candidate for an SBR at some point in the future. I believe these rifles are blowback-operated, as opposed to direct impingement like most other ARs. With this type of system, would there be anything to SBRing it (other than the tax/legal aspect) besides just chopping the barrel and rethreading for the flash suppressor? If I go this route, I would almost certainly start with the 16-inch barrel and carbine handguard. If I like the platform and it's reliable, then I could cut it back to 10 or 10.5 inches once the paperwork is cleared. Mechanically, is there anything more to it than that? Thanks.
  2. BLAKEinTX

    BLAKEinTX Well-Known Member

    Nope just chop, recrown, and thread its pretty simple

    I would get a can also it pretty fun when you have a 9mm pelletgun

    I would get like a midlength freefloat tube or rail to cover up most of the bbl and give it a sleek look since you dont have or need a gasblock because they are blowback
  3. rjrivero

    rjrivero Well-Known Member

    You'll love the SBR 9mm AR. You can chop it as short as you dare without worries of function. A great host for suppressors as well.

    Do you shot Glocks? If so, consider making a DDLES lower part of your 9mm AR build. The fact that it uses Glock Mags makes it much more useful, imvho.


  4. minutemen1776

    minutemen1776 Well-Known Member

    RJ, I shoot a Glock 19, so the DDLES lower would be an excellent option for me. A complete lower runs about $500, which isn't too far from the RRA lower. However, what type of upper will the DDLES lower run with? The only thing I saw on the site was a $1,000 custom upper.

    BTW, I saw that DDLES offers engraving on their lowers. Do I recall correctly that an SBR has to be engraved in some fashion? How does that work?
  5. BLAKEinTX

    BLAKEinTX Well-Known Member


    (dont have to be in all CAPS lol)

    I think if i remember correctly that DDLES can mod an upper to work with their upper or at least someone offered that
  6. rjrivero

    rjrivero Well-Known Member

    To run a single feed magazine you can use any Colt style upper. You just have to have the bolt milled narrower to fit between the feed lips of the Glock magazine. There are many places that can do that for you, but I use Adco Firearms in Sylvania, OH.

    You can use a Colt, or Rock River Arms uppers. I built mine with a Rock River upper.

    Engraving your lower as per ATF 5320.8 means you have to have the name of the entity making the SBR (Either your name or your trust/LLC name ) and City, ST. (As Blake noted above.)

    The engraving must be .003 Deep and 1/16" tall. SEE ATF 5320.8.

    I only have a picture of my Lone Wolf lower AR (now two years old), but the DDLES is a nicer product (Still waiting for my form 1 for it). 9mm AR's are A LOT of fun!

    Blake: I gotta get a picture of it with my Mystic on it. It's a great suppressor for these AR's ;)
    Last edited: Aug 3, 2012
  7. MasterSergeantA

    MasterSergeantA Well-Known Member


    Is the bolt the only modification that has to be made to run the Glock lower? A couple of guys here in my shop have been toying with the idea of using those since the guy is local. I was going to run an ASA side-cocking upper as well with a 7" barrel I got from Mark McWillis.
  8. rjrivero

    rjrivero Well-Known Member

    Yes. The only thing you'll need to do is mill the bolt narrower. I prefer to ramp the bolt as well, but that's optional to reduce stress on the hammer pin.

    This sounds like a great project. Can't wait for the pictures!!
  9. minutemen1776

    minutemen1776 Well-Known Member

    Thanks for all the helpful info. As I continue to look around, I see more and more options available for 9mm ARs, but it's hard to know exactly what parts are compatible with one another and what would be OK for an eventual SBR conversion.

    I see that CMMG now makes a good-looking 9mm complete lower that runs about $300. Are these compatible with Rock River 9mm uppers? Some of what I've read seems to suggest that a different hammer might be needed, but I cannot be sure. I ask all this because I'd like an upper with an A2 carry handle, which CMMG does not offer.
    Last edited: Aug 3, 2012
  10. MasterSergeantA

    MasterSergeantA Well-Known Member

  11. minutemen1776

    minutemen1776 Well-Known Member

    The FAQ is very informative. It appears that CMMG makes its 9mm uppers with a ramped bolt, therefore requiring no special hammer. I'm assuming, then, that their 9mm lowers come with a standard AR hammer. If so, I'm thinking that I'd need to retrofit with a special 9mm hammer if I decided to install a RRA 9mm upper (and specifically a RRA 9mm bolt) on a CMMG 9mm lower. Right?
  12. rjrivero

    rjrivero Well-Known Member

    All you need is a hammer without the notch. I don't have any "Dedicated 9mm Hammers." Just the Smooth top ones.

    Like the one in the middle of this picture. The one on the right will hang up on the bolt and jam up the works. Leave them out of your 9mm build.

    Left to Right:
    M16 Hammer with "Rat tail" removed
    Smooth top hammer (From DPMS)
    Rock River AR15 Hammer

  13. BLAKEinTX

    BLAKEinTX Well-Known Member

    Hey RJ have you sent that pic in with the mystic on if you email it to us or post it on our FB page you can be entered to win a free shirt or hat

    The Mystic is a badass can but if i had to pick between the Mystic and Infiniti i would choose the Infiniti its stupid quiet with my 147gr reloads and a little remoil

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