I posted this on my RXM Thread over at GlockTalk. Updated and most recent range rep:
Ok, BIG UPDATE and RANGE REP: I traded something in and got a SECOND RXM. Yeah, because I'm stupid, and I wanted one.

Or I love the gun, and I'm gonna be investing in the infrastructure of this platform, so having a second FCU or FCI or whatever they call it is gonna be RAD. The cost on these isn't prohibitive, and with my trade in I didn't have to pay much more. I enjoy the hell outta these things, so it came naturally to me.
So, the same PMAGs are still having issues in the new RXM... Except the
PMAGs that it came with are not. Why? I looked very closely at the now 6 PMAGs I have; I sent 3 back to Magpul for their engineers to review soon. Here's all 6, next to each other, as leveled as I could get the photo, with a solid white background. Notice anything?
Yeah, the 3 PMAGs on the
right are presenting the rounds higher. You can literally see a small, but very important difference. Even the feed ramp is physically higher in the front, than the 3 on the left. Took them apart, and I'm not able to really discern any major difference. The followers have some minutely different markings, but not consistent among the good vs bad PMAGs. The springs were a little different, but still. I'm gonna be presenting this to Magpul, as well. They've been awesome, but they're leaning towards it being the gun. It's not.
I ran the exact same break in test; no cleaning the new RXM since I didn't clean the first one, and the manual says take it right to the range without cleaning. It ran with 100% reliability, with the 2 PMAGs it came with and that 1 out of the 4 PMAGs they sent that seemingly works, too. Zero nosedive failures, or any other kinds of failures.
Same 100+ rounds of Magtech 115 gr JHP, and 200 rounds of S&B 115 gr FMJ. I ran this test even faster than the first RXM's testing, and the gun got uncomfortably HOT at a couple points.
Also, for good measure, I brought RXM #1 and ran one mag of the Gen 5 Glock 19 through the new RXM #2, and vice versa. A PMAG of the same JHP (one of the working PMAGs) through RXM #1. All smooth sailing, zero malfunctions. It's the PMAGs having differing tolerances, period.
The RXM is a great shooting gun, and I decided to get another one to really run my own test series. All the shops I go to in my area are sold out, and my main Sportsman's showed them in stock. When I went in, I asked how many more they got and they told me they had ONE left. They're selling rapidly. I also decided to get a second RXM, as I'm hopeful that the accessories infrastructure for these from Ruger and Magpul grows rapidly; frames, different slide lengths, the sky is the limit. If it doesn't, this thread won't go anywhere and y'all can make fun of me

If it does takeoff and be a hit like I think it will, I'll already have a tested, reliable secondary.