Quarter Circle 10 MP5 AR PCC | SHOT 2017

Quarter Circle 10, the Pistol Caliber AR company has made a name for themselves with their Glock mag fed ARs. Now they have made a lower that can use MP5 magazines. With ETS making MP5 magazines, I think these will be a hit.

They also have a different side charger on the upper receiver.

Nicholas C

Co-Founder of KRISSTALK forums, an owner’s support group and all things KRISS Vector related. Nick found his passion through competitive shooting while living in NY. He participates in USPSA and 3Gun. He loves all things that shoots and flashlights. Really really bright flashlights.

Any questions please email him at nicholas.c@staff.thefirearmblog.com


  • hami

    I don’t want to take away from how awesome that is… But I do wish they could have engineered a paddle release into it.

  • Shankbone

    This headline did weird things to my heart when I saw AR, PCC, and 10 in the same line.

  • Nicks87

    This is cool but MP5 mags are expensive and do not share commonality with any pistol. Glock mags FTW.

    • int19h

      This can change literally overnight if Magpul decides that it’s a worthwhile market to pursue. Which, seeing how many MP5 clones and gadgets for them are being shown these days, sounds like it might be. Even more so if SBRs are removed from NFA.

    • How many people actually need mag compatibility between their long gun and pistol. Have you ever loaded MP5 mag? Loading single feed large cap mags sucks, the dual position SMG mags are so much easier.

      • Nicks87

        33 rnd Glock mags load just fine and I’d rather not buy more mags then I really need. The fact that so many weapons use Glock magazines probably means that this is a desirable feature.

    • Corwin Bos

      You can find 30 rnd MP5 mags for $25-30 a piece if you shop around. Yes they are not HK branded, but they work just fine. For 9mm the forward curve is actually ideal due to the taper of the case. And not everyone wants a Glock…

      Colt and Glock mags will also fountain if you drop them when loaded. Ive only had it happen once with my Colt SMG mags which are Metalform from PSA. I have seen Glock 30 rnd mags fountain as well. The MP5 mags will not.

      I use Colt mags in my AR9, and once you get to about 20 rounds, they are a PITA to load. Which is why I use a MagLula. 30 round Glock mags also get pretty tight post 20 rounds.

      I was actually waiting for this lower, but didnt want to wait another year, so I went with a Colt lower from QC10

      Please do a little research before spouting randomness…

      • DataMatters

        Where? I have two curved 30s that I bought for $55 years ago. Haven’t been able to get my hands on any since. I have some straight ones, too. A bunch of those came in like 10 years ago and I grabbed a bunch. But I can’t find curved ones at all. And didn’t HKPRO go out of business or the owner got arrested or something sketchy?

        • Corwin Bos

          Just google korean MP5 mags. I tried to post a link to AIM Surplus, but it didnt want to go.

          • Nicks87

            Korean junk. If you have the money for an MP5 or clone then you can afford to buy real ones. Dumb.

      • Nicks87

        Spouting randomness? WTF? I think my point is valid. Show me a pistol that uses MP5 mags and is not an MP5 without a stock. I’ve never seen 33 rnd Glock mags do anything except function as advertised. They were probably Korean knock-offs that were “fountaining”. Whatever the hell that means.

        • Corwin Bos

          I will agree with you, no pistols that use MP5 mags are out there.

          I have seen Colt and Glock 30 32 and 30 round mags fountain. Fountaining is what happens when a slight jar to the mag causes all the bullets to fly out. Neither the Colt or Glock mags work perfectly because when you load a cartridge like a 9mm that has a slight taper to it, into a mag that attempts to hold them all straight, it creates problems. The MP5 mag do not suffer from this because of forward curve which allows the bullets to be in the mag with no issues caused by the taper. It doesnt happen in regular mags because the spring tension is not nearly as high as a 30+ round mag.

          As far as Korean knock offs of MP5 mags goes, other than the fit and finish of them, you wouldnt be able to tell they are not HK mags purely on the one thing that counts, do they work? If they work, then why not buy 3-4 Korean made mags for the cost of a single HK? Im not that much of a brand snob that I need a certain brand of mags. I buy what works, pure and simple.

          Last question? Do you actually own an AR chambered in 9mm? For those of us that are looking for 100% mag reliability, being able to use a very well designed HK mag in this platform IS a huge deal because they DO work better than Glock or Colt mags. And this is coming from a guy that owns a dozen or so Colt mags made by Metalform and 20 or so S&W M&P factory mags. You obviously own Glocks, your fanboi is showing.

          • Nicks87

            Only time I’ve ever seen the rounds come “flying” out of a dropped loaded mag it was caused by the base plate coming off. Never has it happened with a Glock magazine and I’ve dropped plenty of them. No I do not currently own a 9mm AR but when I do it will use Glock mags and yes I am a Glock fanboy.

          • Corwin Bos

            It never happens with the regular mags, only with the 30 rounders. Like I said, alot more spring pressure on the 30 rounders when they are full is what causes it.

  • Matthew

    different upper, different lower…why bother???
    just make an MP5 clone…

  • Big Daddy

    I need this……..very badly…..I must have this.

  • Twilight sparkle

    Wait… bolt hold open??? Does… Does it actually work?????

    • Guessing its only there for manual locking it back since I do not think they can get it to work with MP5 mags unless the mag was modified.

      • Twilight sparkle

        That was my thought exactly

    • Corwin Bos

      I own a QC10 lower that uses Colt SMG mags, and I can confirm that LRBHO does indeed work. Their lower that use Glock mags also have working LRBHO. I cant imagine that they would put something out there that doesnt have it.


        MP5 magazines have nothing to use as a LRBHO into the magazine follower.

        • Corwin Bos

          Time will tell. They were able to make it work with Glock and Colt mags. These have been on the drawing board a couple times, so Id bet they got it working.

  • stu reder

    How about making a model to fire the 10 mm? I could be talked into purchasing at least one.

    • William Johnson

      I got to fire one of their models in 45 (used glock mags) at the Firearms Festival in TX, it was accurate and handled well. They stated that once they moved their production facility they would begin offering the model in 10mm (again using glock mags). I am a potential future customer.

      • Mazryonh

        Ever since H&K stopped making their MP5/10 there’s been a serious gap for SMGs in 10mm. Time will tell whether a QC10 in that caliber will actually sell well.

  • Fox Hunter

    But like most AR PCCs, it aint ambi. The ARmini is better cause it is ambi mag and bolt release.

  • Lou

    Not a bad idea!

  • Michael Stroup

    This is awesome, especially since there is that company that makes MP5 uppers for AR15 lowers. Did someone say easier MP5SD?