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Thread: AR9

  1. #1
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    AR9

    I built an AR9 with a BCA bolt and barrel. I wanted to use regular Magpul 5.56 mags so I bought a Mean Arms pmag converter. I knew going into this I could possibly have trouble with feeding and cycling. I tested fired it yesterday, it had a lot of trouble. The mag would barely fit, I would have to press it very hard for it to seat. Every round that fired the mag would fall out, I noticed wear marks on the notch of the mag. I went home and dremeled that mag notch about a 1/16" and went back out later for another test fire. Now the bolt will not pickup a round from the mag, I must of taken too much off the notch in the mag. I am not very impressed with the Mean Arms mag converter, the feed ramps and ejector are made of plastic and took a beating with only about 10 rounds fired. I would say that after a few hundred rounds it would all be worn out the the point it wouldn't function anymore. I'm going to continue to work on this thing to get it running reliable but I would like to go a different route with magazine.


    A few years ago I saw a similar mag converter to Mean Arms. It was like a block type device that fit in the mag, using it's current spring and follower. I just can't find anything like it, all that comes up when I search is the Mean Arms and the CMMG converters with are almost the same except the CMMG with only work with a proprietary CMMG upper. Does any body run this setup or one like it and if so what are you using?
    Last edited by december1979; 03-09-2020 at 01:34 PM.

  2. #2
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    I have 2 AR9's set up for endomags. Have 6 mags. They all work great. In my case they prefer to be clean or the occasional FTL will happen. Otherwise they're a blast. Is your bolt ramped?

  3. #3
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    The barrel has a slight ramp, not sure what you mean by ramped bolt, I think you meant barrel. When I first had it all put together I hand cycled 10 rounds and it chambered and ejected all of them. Live fire was a different story. It seems like the ejector is making contact with the bolt so the mag it barely seated so when the round fires it flies out. I read on other forms this is a common problem and people have shaved down that ejector and it seemed to help.

    What bolt are you running in your AR9's?

  4. #4
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    I have a foxtrot Mike fm9 bgc and a Karris guns bcg. Both are ramped... Has more to do with trigger reset. Try polishing the barrel feed cone to a mirror shine. That definitely helped me.

  5. #5
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    The bca ar9 only works with Glock mags. I found out that the hard way last month.

  6. #6
    MGO Member JDG's Avatar
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    The only AR9 that ever ran 100% for me was a Frontier Armory C5, that ran MP5 mags. All the others I've tried were project guns, needing tweaks...
    Active airport shooter

  7. #7
    MGO Member Moleman-'s Avatar
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    My first 9mm ar15 was a cheap DI upper built with left over 223 upper parts (opened up the bolt to fit 9mm cases), a $30 barrel blank, sten mags and a self made magwell block and super short gas system. Worked but was finicky. First blowback used the sten mags and self made magwell block and a barrel made from a Green Mountain blank that I just copied a Sten MK2 feedramp on. Worked better but sten mags vary enough that they're not an ideal solution. Some would fit, others wouldn't and the feed lip shape and width also varied. So onto one of the Colt pattern magwell blocks and mags. Worked well enough that eventually my father in law wanted one so we pieced one together for him one year using a BCA barrel. It didn't feed for squat because the BCA feed ramp was smaller and a more flat angle. Recut it to match the Sten style and it fed much better. Ended up giving him my magwell adaptor and that 9mm upper since they worked well together and they made their way back to us when he passed. I was going to get another magwell adaptor but found CMMG dedicated lowers on sale that were about the same price as an all metal colt style magwell adaptor (cheaper than the RRA adaptor) and the metal C-products 32rnd mags are about $18 each which isn't bad. Fun range plinking guns that are cheaper than a 223 with little recoil while giving you the feeling that you're not just shooting a 22LR.

    FWIW the other BCA barrel I have is a AR10 pattern 308 barrel that sat on top of my bench for two years before it was installed. It won't easily chamber factory ammo and those that do chamber are left with rings/gouges on the shoulder area from a rough chamber, so I haven't shot that barrel.

  8. #8
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    Quote Originally Posted by JDG View Post
    The only AR9 that ever ran 100% for me was a Frontier Armory C5, that ran MP5 mags. All the others I've tried were project guns, needing tweaks...
    Funny thing is that was my C5, I bought it from a guy in Muskegon and changed out some internals and replaced the muzzle break with the intention to run a suppressor. A 1911 Colt Combat came up on Armslist and I could not resisit and traded it. I saw it come up for sale on Armslist a few months later.

    I seen you had it for sale here
    Last edited by december1979; 03-30-2020 at 02:16 PM.

  9. #9
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    Quote Originally Posted by Moleman- View Post
    My first 9mm ar15 was a cheap DI upper built with left over 223 upper parts (opened up the bolt to fit 9mm cases), a $30 barrel blank, sten mags and a self made magwell block and super short gas system. Worked but was finicky. First blowback used the sten mags and self made magwell block and a barrel made from a Green Mountain blank that I just copied a Sten MK2 feedramp on. Worked better but sten mags vary enough that they're not an ideal solution. Some would fit, others wouldn't and the feed lip shape and width also varied. So onto one of the Colt pattern magwell blocks and mags. Worked well enough that eventually my father in law wanted one so we pieced one together for him one year using a BCA barrel. It didn't feed for squat because the BCA feed ramp was smaller and a more flat angle. Recut it to match the Sten style and it fed much better. Ended up giving him my magwell adaptor and that 9mm upper since they worked well together and they made their way back to us when he passed. I was going to get another magwell adaptor but found CMMG dedicated lowers on sale that were about the same price as an all metal colt style magwell adaptor (cheaper than the RRA adaptor) and the metal C-products 32rnd mags are about $18 each which isn't bad. Fun range plinking guns that are cheaper than a 223 with little recoil while giving you the feeling that you're not just shooting a 22LR.

    FWIW the other BCA barrel I have is a AR10 pattern 308 barrel that sat on top of my bench for two years before it was installed. It won't easily chamber factory ammo and those that do chamber are left with rings/gouges on the shoulder area from a rough chamber, so I haven't shot that barrel.
    I did notice the feed ramp on the barrel was very small compared to all the pictures I have seen on other 9mm barrels. I have since sold the AR9 upper, I went back to a 300 blackout, but did not use a BCA barrel, I went with Ballistic Advantage barrel. I'm very impressed with the quality.

  10. #10
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    Quote Originally Posted by JDG View Post
    The only AR9 that ever ran 100% for me was a Frontier Armory C5, that ran MP5 mags. All the others I've tried were project guns, needing tweaks...
    About 4 or 5 yrs ago I bought a STAG 9mm ar that used colt style mags. Not a single bit of trouble out of it. ASC mags run like a champ. 10, 20, or 32 rd mags were Around $13 -$16 last I bought any.
    I might have been able to "build" one cheaper but I wanted one that works without fussing with it.
    Just because something is legal to do doesn't mean it is the smart thing to do.

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