I have some of their 7 8 and 10 rounders. The 7's are 100%. I've had a jam or 2 with the 8's when I stuff 8 in them. The 8's are 100% with 7 rounds. The 10's, well, I had to do some work there.
I think the 10's will be OK as they break in. They are real stiff at first and I'm letting them sit for a month or so stuffed full of ammo.
The lips on the 10's weren't smooth. I stripped them and took scotch bright (real fine type sandpaper stuff) to the lips. It took a long time but now the bearing surface on the lips is slicker than baby poop.
I didn't have to do any drop free "fitting" with any McCormick mags. They all worked fine in that respect.
Nobody's mags are perfect all of the time. A friend of mine even had a bad Wilson, the follower would lift the slide stop before the last round fed. I had 1 Wilson that required a new follower also. No problemo, the company sent out new followers for free.
I'll give McCormick 7 round mags 10 stars out of 10.
I'll give McCormick 8 round mags 8 stars out of 10.
I'll give McCormick 10 round mags 7 stars out of 10.
Wilson 7 round combat mags get 9 stars out of 10.
King's 7 rounders get 10 stars out of 10.
Well, at least that's what I think anyway