Delete.

Both my S&W 5.45mm uppers worked OK, but I have seen one or two which appeared finicky. I was always able to utilize G.I. 5.56mm magazines by downloading the twenties to 17, the thirties to 25 or so. YMMV, others haven't had as much success, dunno why.

Had one good & one bad C-Products 5.45 mag, each upper came with one when I bought 'em. I also concur with the 80% statement above. And yes, Russian ammo is filthy stuff ..........................

I have five rifles in 5.45mm made in different countries. None keyhole, nor did either of my S&W 5.45 uppers when I had them. With multiple types of commercial & military ball. Plus some HP & SP.

A bullet which keyholes will not be delivered accurately. The projectile is designed to upset & become unstable when it strikes its target, not while it's in flight. Keyholing is a result of Americans failing to properly build a 5.45mm barrel.
I.e., Century's (should never have happened) fiasco with its first Tantal builds.