Here's my Umarex .22LR (SureFire M63 Rail, Kac Rails and Forearm Grip, Gear Sector Hand Stop, MFI Optic Rail, Aimpoint M4s):
Shot close to a 800 rounds today and the rifle shot pretty tight groups with the red dot. Stock irons shot about 3" high and to the right at 25 yards. Didn't have the proper hex wrench and philips screwdriver to adjust the windage so didn't fiddle with the irons at all.
Out of 440 CCI Mini-Mags, had one where round wasn't stripped off the magazine to the slightest, but had a slight scoff mark where the bolt moved over it. Not sure if it was the bolt or if it was a magazine issue.
250 Wolf Match Target had 1 where the round didn't make it into the chamber and got bent out of shape. On the final round of the 250, the bolt didn't move far back enough to eject the round or actuate the bolt catch.
100 Fiocchi round nose ammo went without a hitch.