OK, I took the gun apart and cleaned it. I compared the receiver to my 551s. There is a hole at the bottom just before the chamber. I guess this is for over pressured rounds (so it blows out down away from the shooter)?
Attachment 71403
Note the barrel was marked 2019 but my receiver is 2021 (not shown). Kind of cool given the pandemic and how they have to batch things.
Here is the chamber. Compared to my 551, the feed ramp looks the same and is quite small. There is not much of anything between the feed ramp and the chamber, unlike the feed ramps on the M4 or an AK bullet guide. I’m just used to seeing large riveted bullet guides on my AKs. That’s all. I just think it didn’t like Tula:
Attachment 71404
That’s the best picture I could take with my iPad. Moving on, look at the lower receiver. There is little lateral play with magazines. There is a large amount of forward and rearward play with the magazine however. This was a hard picture for me to take, but here is the Magpul MOE magazine resting naturally without any pressure on it:
Attachment 71405
Now watch it when I use my finger to push the magazine forward in the lower receiver:
Attachment 71406
I can do this with the steel magazines and commercial Bulgarian magazines. Not so much with the Circle 10 magazines though. I’m guessing this was by design? Once I SBR the other 553R I bought, I’ll take it to the flat range, shoot prone, and see if magazine pressure induces any malfunction. I’ll just have to stick to brass cased ammo or good quality steel cased ammo (lacquer coated, good stuff like Barnual manufactured).
Regardless, it’s nice little pistol. Needs a tax stamp.