AR 15/9 question

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  • outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,818
    It won't work with RDB, your gun will short strike, guaranteed. In fact, I bought one and it didn't even work with regular direct blowback. I think maybe it could work for some people, but I wasn't impressed.

    Some of the dudes on Brian Enos have started experimenting with this one, which is roller-delayed, and it sounds like it works better than you'd expect:
    http://scheelmfg.com/

    Does it handle full power loads?
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    Alucard likes it. Maybe he’s in the minority
    I had serious issues with the gun doubling on me. Given how wildly tolerances can vary, I don't think it's unrealistic that someone else's gun could work better with it, but I went as far as replacing my entire bolt assembly and the FCG to try to make that thing work, and it didn't. Going to a Taccom 3 stage buffer (and putting the weight back in my bolt) fixed it all immediately.
     

    teratos

    My hair is amazing
    MDS Supporter
    Patriot Picket
    Jan 22, 2009
    59,775
    Bel Air
    I had serious issues with the gun doubling on me. Given how wildly tolerances can vary, I don't think it's unrealistic that someone else's gun could work better with it, but I went as far as replacing my entire bolt assembly and the FCG to try to make that thing work, and it didn't. Going to a Taccom 3 stage buffer (and putting the weight back in my bolt) fixed it all immediately.

    Have you played with the CMMG RDB stuff? I like mine. Especially vs my direct blowback gun. I did buy that roller delayed system. Looking forward to trying it vs RDB.
     
    Last edited:

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    Have you played with the CMMG RDB stuff? I like mine. Especially vs my direct blowback gun. I did but that roller delayed system. Looking forward to trying it vs RDB.
    Not yet, but here's the plan since I now have to care about shooting PCC seriously due to my son shooting it for competition:

    I just bought a Sig MPX PCC. Well, really, a certificate for one from a dude who won it in a match (which I guess sounds suspicious, but I know who he is, and he definitely did win it). Once I've gotten the redemption of that squared away, I'll put it through the usual minor upgrades and testing to ensure 100% reliability.

    Once the MPX is validated, I'm going to be taking apart a bunch of ARs, including my 9mm upper, and selling off a ton of stuff. The funds will be used to get an RDB upper and a bunch of Endomag inserts. That will be PCC #2. Lack of mag commonality will suck, but it is what it is.
     

    teratos

    My hair is amazing
    MDS Supporter
    Patriot Picket
    Jan 22, 2009
    59,775
    Bel Air
    Not yet, but here's the plan since I now have to care about shooting PCC seriously due to my son shooting it for competition:

    I just bought a Sig MPX PCC. Well, really, a certificate for one from a dude who won it in a match (which I guess sounds suspicious, but I know who he is, and he definitely did win it). Once I've gotten the redemption of that squared away, I'll put it through the usual minor upgrades and testing to ensure 100% reliability.

    Once the MPX is validated, I'm going to be taking apart a bunch of ARs, including my 9mm upper, and selling off a ton of stuff. The funds will be used to get an RDB upper and a bunch of Endomag inserts. That will be PCC #2. Lack of mag commonality will suck, but it is what it is.
    I’ll get this roller delayed system in, and make sure it works. I have a RDB and a direct blowback gun. If you want to get together to shoot, you are welcome to try them out.
     

    woodline

    Ultimate Member
    MDS Supporter
    Jan 8, 2017
    1,947
    MP5s are pretty smooth. Some folks don't care much for them, but I've only shot one once, both semi and full auto. I had no complaints. :D

    Teratos and I have been playing around with adapting the RDB for a MP5 AR lower. Best of both worlds. The problem has been getting parts for the last couple years...
    I have a good amount of time behind select fire MP5s, MP5Ks, and MP5SDs, but you really have to shoot stuff side by side to see if there’s any major difference. Semi auto I don’t think recoil will be much different, especially with the hydraulic buffer in the RDB setup I’m running. It’s definitely less gross than an MP5SD setup. Those barrel ports tend to clog pretty fast, especially with frangible training ammo like I have to use, and then southpaws like me start getting debris in the teeth. At any rate 9mm ARs destroy MP5s in ergonomics at the expense of overall length, but it doesn’t matter much for my use case.

    Good luck with your MP5 mag project, that would be cool to see, and you could definitely make money off of it if the mods aren’t too extreme. I know some folks have been trying to adapt the RDB system to use Scorpion mags with mixed success. I want to say the guy who had the best luck could only use one type of mag, maybe Scorpion Pmags. I’m happy with the endomag modded PMags, since it keeps things modular and let’s me use the same pouches. But if CMMG ever made an RDB system that took scorpion mags, or if mean arms ever gets their roller delayed AR upper on the market, I would definitely be interested.
     

    woodline

    Ultimate Member
    MDS Supporter
    Jan 8, 2017
    1,947
    Look, I know this is a controversial statement, but of all the 9mm mag choices, Colt-style is the worst by far. A quality Glock lower is far better in terms of just being able to buy a factory mag and have a reasonable expectation it will function without extensive QC testing, never mind the whole magblock situation.

    If I were doing it all over again from scratch - and I might be, come to think of it - I'd go with either a proper CMMG MkGs RDB Glock mag receiver set, or I'd go with a standard lower and use Endomags (which I have mixed feelings about, but they clearly work well in an RDB setup). I would not go direct blowback again.
    The endomag adapters for RDB lack the major weakness of the direct blowback version, but I can’t help but feel as though they are janky just because they are an adapter and not a native magazine. So far I’ve not had issues, but even if I never experienced a failure I’m not sure I would ever feel like they were good for serious use. But for training and competition, I think they’ll do fine. I am also probably in the minority in that I don’t really care to use glock mags, as I’m stuck either building/buying a new RDB compatible lower, or using some magwell adapter that I trust far less than the endomags.

    The fact that I can build an upper to basically mirror a serious use upper, and then use the same lower with no mods, same kit, same belt, etc counts for a lot for my specific use case. But those mags sure do take up a lot more room than they need to.
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    Using AR mag pouches, to me, is actually a pretty nice bonus for the Endomags. Don't have to reconfigure my belt to use PCC magazines, just stuff a couple in my AR pouches and go to work.

    I don't even know what I'll do with the DDLES lower... probably just stuff it in the safe and wait for someone to come up with a delayed-blowback system that actually works with it.
     

    teratos

    My hair is amazing
    MDS Supporter
    Patriot Picket
    Jan 22, 2009
    59,775
    Bel Air
    Using AR mag pouches, to me, is actually a pretty nice bonus for the Endomags. Don't have to reconfigure my belt to use PCC magazines, just stuff a couple in my AR pouches and go to work.

    I don't even know what I'll do with the DDLES lower... probably just stuff it in the safe and wait for someone to come up with a delayed-blowback system that actually works with it.

    I run a DDLES Colt pattern lower on a RDB upper. You just need to file a 10th of an inch off the top of the mag catch so the mag sits lower. Runs great.
     
    Ive built one that takes glock mags. If i had to do it again i would not use glock mags. Because of the glock mag design the round has to "jump" about 4/10ths of an inch to enter 5he chamber. It causes a lot of feeding issues. I used a Taccom feed ramp to fix the feed issues .. it works but i still wish i would have used colt or S&W mags.

    https://www.google.com/url?sa=t&sou...0QFnoECAcQAQ&usg=AOvVaw1nANhG8L2HUPvtfMscy1D2
     

    m.ammer69

    Member
    Jul 3, 2013
    76
    Thank you guys for all of your suggestions on part s,I have lots to look through. Did I also see someone mention an AR-15 that fires a 45acp?
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    Alucard likes it. Maybe he’s in the minority.

    I like the Taccom short stroke system, cuts the stroke down to 2" and reduces recoil/movement substantially, but still plain blowback, I use a 10oz KVP buffer and 308 spring with mine. Only downside is it's hard on triggers, and many won't work or will hammer follow with it. I have tried their "magnetic delayed blowback system", and didn't really see a difference. I'm really curious about that Scheel roller delay though, that looks VERY promising, would love to hear your thoughts on it after you try it out, might snag a couple myself. The main issue with the RDB is that it uses a full length stroke, and the feed geometry with 9mm is goofy. The couple I tried weren't all that impressive compared to the blowback systems I run in my PCCs. The roller delay in the buffer/tube completely solves that, and could be the best of both worlds, short stroke, good feed geometry, works with standard blowback 9mm lowers/barrels/bolts.

    As far as the OP goes, there are 3 ways to convert an AR to feed 9mm rounds. Endomags are the simplest, standard lower, the mags handle the feed and ejection, build any upper with a 9mm blowback barrel/bolt/buffer system.

    Use a mag adapter with AR15 lower, the adapter handles the feed/ejection, but with less expensive Glock or Colt/modified UZI mags.

    Dedicated lower, feed and ejection are built into the lower. Simple, control layout works for the GLOCK, COLT or whatever other mags you use.

    With any system, the last round bolt hold open is probably the feature that varies the most, some don't have one, some have one that never works, some work 100%. Colt pattern lowers and adapters work well, some GLOCK pattern that use a rotating linkage(FM products) or wire linkage in the upper(Aero) work very well, those with a long lever in the lower(QC10/most GLOCK magwell adapters) usually are less than reliable.

    If you want a replica M16 or M4 chambered in 9mm, the COLT setup is the way to go, there were plenty of Colt AR9 models produced too. THe mag sits twards the back of the magwell, and feeds from the double stack mag across a feed ramp into the chamber. Most issues are from mags, buffers, or the relatively long distance the round has to travel from being pushed out of the mag, funneled in the feed ramp, and forced into the chamber.

    GLOCK mag AR9s are responsible for the 9mm AR platforms current popularity. Colt AR9 rifles have been out for decades, but heavy recoil and reliability issues kept people away. GLOCK pattern AR9 have the mag that feeds from a single point in the front of the magwell near the chamber, eliminating the feed ramp and dual stack feed points of the COLT. It's more reliable, simpler, and can run off of a shorter stroke.

    In either setup with blowback, the shorter BCG(lacking a bolt/locking lugs) needs a spacer or longer buffer to keep from moving too far and slamming into the bolt catch with enough force to break it. a full 4" stroke isn't needed with short 9mm rounds, most limit it to 3", the minimum for most 9mm bolts to clear the bolt catch. Some short stroke bolts use a notch in the bottom of the BCG to engage the catch, and only have a 2" stroke to cut recoil and movement further.

    Most AR9 blowback tuning involves tuning reciprocating mass to give an appropriate bolt velocity. When fired the case expands and locks into chamber till chamber pressure drops and it can "blow back" against the unlocked bolt face and cycle. The bolt/buffer mass controls velocity, spring rate can help slow it it to a lesser degree, and power the feed stroke. THe downside is the roughly 24oz of bolt/buffer mass can have more recoil than rifle calibers using DI with a locking bolt. There are also some innovative systems using hydraulic buffers, magnets, or as referenced above roller delay mechanisms to better control the timing with less mass and lighter springs.
     

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