As someone who is autistic about insisting that rifles and SMG's do "double stack/double feed" for reliability reasons, I have to inform you that NEW Uzi Pro magazines (which are cut for the old Uzi mag catches, too) are CHEAPER than Glock mags. Yes... "when available" but when they do a batch, you pick up 5-10 of them at at time as a proper gun autist should. The only real reason to have an AR9 running glock mags is if you're lazy and already have a ton of Glock magazines.
I've never had a Glock 33 stick fail on me. On the same subject never had a factory parts Glock malfunction on me, I'm convinced he limp wristing thing is an urban legend at this point. I have a Gen 2 27 I have shot with thumb/index finger alone at least 10 rounds and never got it stovepipe with winchester white box range ammo. I've owned 3-4 Glocks over the years. It's like a 2005 Toyota Camry, it has no soul, you won't impress anyone women with it and it's painfully boring to drive but it makes it to 350,000 miles if you change the oil.
As far as I could tell the UZI mag lowers were not compatible with the CMMG Radial delayed upper due to the feedramp design. I might be wrong. From an engineering POV I never liked the huge "jump" the 9mm cartridge had to make between magazine and chamber. I cannot picture a factory made gun that has anything resembling that big a leap where the cartridge is neither controlled by the magazine or the feed ramp/chamber for even a fraction of a second.
I know if I flip a glock 17 or a CMMG glock 9mm upside down, magazine pointing towards the sky and ride the slide/BCG by hand as slow as possible forward till the round is fully seated it's still going to be seated. Gravity and speed of chambering makes no difference. I take a colt pattern 9mm AR and do the same I'm pretty sure the round is flopping up getting jammed in the charging handle area or something. I regret not testing this theory.
For all unfamiliar there is about a .750" long feedramp with wings in the original Colt adapters. A quick google search revealed there are apparently half a dozen different companies making or at least selling 9mm mag adapters but all the Colt/UZI pattern mag adapters follow the same pattern of a big jump between the magazine letting the cartridge free and the chamber and requiring guiding "wings" as part of the feedramp.
The double feeding mag and the LRBHO were the only two things that made the Colt/UZI mags seem like the better design. I never got my LRBHO to work reliably.
Colt SMG mags are based off of UZI magazines, iirc, so if you're in a do it yourself mood you can pick up a stack of surplus Uzi mags and a template and cut the mag catches yourself.
Those CMMG endo mags are pretty neat, but if I were going to use those, I would get something like clear PMags for the bodies just so that you can tell them apart from your 5.56 magazines at a glance (when loaded).
Being a proper firearms autist I already had a fagctacular Semi auto closed bolt UZI I welded together years ago from a parts kit, and a handful of surplus UZI mags I then I modified with a 1/8" end mill for an AR mag catch. The cucked UZI... OMG so disappointing when it was done VS a real Tax stamp NFA UZI. The days spent just tuning the semi auto hammer system so it would run reliably were days I'll never get back.
I go to the range get a 1-2 or two people "oh shit, is that a Pre-86 FA UZI"!? Then they see it's just a lame 8lb pistol. AFAIK I'm not even allowed to keep the original FA open bolt that came in the parts kit, in the same location as my SA closed bolt gun as that would be considered "constructive intent" or something. Doesn't it work like that with AR's? If you had surplus M16 FCG in the same house as an AR it was theorhetically prosecutable offense? The alphabet gang thought it was to easy to drill the forbidden hole and drop in a true FA FCG, yet you can just buy a set online for 100$ unless that's bait or something. IDK, I'm not interested in finding out. So I guess I'm waiting on the days till someone makes an UZI forced reset trigger system or another legal loophole. The fucking gun laws both federally and even in the more reasonable states make no sense.
I have to admit the the CMMG Endo mags are creative, I have never played with them, I can't speak to reliabilty I just find them extreamly bulky for a magazine that holds 30 rounds of 9mm. A 3X 30 round 5.56 Magazine carrier doesn't fit anywhere but a chest rig. Meanwhile 90 rounds 9mm can be slung in a pouch or if you want to go Mall ninja, they can go on the waist or thigh rig. Stanags and Pmags are bulky. Too much wasted real estate.
