While it's somewhat common for semi-automatics to behave finicky when hollow points are involved; in my nearly 40 years of shooting, I've never experienced such behavior with full-metal-jacket ammunition—that is until the other day.
For whatever reason, my U.N.C.L.E Special didn't care for the flavor of FMJ ammunition I gave it the other day. So, yesterday I switched back to Hornady Critical Defense. Despite being the same weight as the FMJ, Critical Defense performed hassle free with a standard 8-round magazine. Up to that point, performance had been mediocre, with tendencies to nose the tip of FMJ ammo either under the lip of the barrel hood or impact directly into the feed freed ramp. The good news is, most often the malfunction can be cleared with a slight pull on the slide to guide the round up the ramp sending the pistol into battery (which is what made me suspect the pistol was short stroking earlier in the week).
I haven't had a lot of time to test the extended-capacity magazines. Although considering the gun's reaction to the FMJ, I did add some shims in an effort to enhance the reliability of the magazines. With a little luck, I'll find some time this afternoon to test the magazines using Critical Defense.
Given the carbine's issues with malfunctions, I think it best to resolve all issues pertaining to reliability before resuming the accuracy test; (although, the initial tests with the spring washer added to the scope mount's thumb screw appear quite promising— thanks, Paul and Eric).