Sounded to me like a mag problem, but I've used PowerMags myself now for years, without any troubles at all in my "loaded" Springfield.
Mine itself took about 300 rounds to "break in", plus a vow to NEVER use "Win Clean" ammo again.
First thing I think I'd try: downloading the magazines by one shot initially. There are a couple of custom fgolloweers that might help, too, but it does sound like a *new gun* problem.
In breaking in a new gun, I tend to do a lot of initial shooting with magazines loaded with 3 rounds anyway, getting more practice in fast magazine changes. The last time I was given a new .45 to wring out and see what I thought of it, I recall putting about 8 boxes through before it settled down into the usually exhibited M1911A1 reliability.
BTW the factory recoil spring weight in a GI M1911A1 is 16#. An 18-pounder sound fine and just a bit of a fudge over the line. But maybe initially, until the rest of the gun's worn in, it might be worth a try with a specified 16# spring.
He said the problem went away if the mags were only loaded with six shots each. I've no idea if the Mil-Spec Springfield uses a 16 or 18 pound recoil spring...I do know that my "Loaded" one uses 18#.
It sounded like he chambers the first shot from the mag himself, fires it, and number 2 hangs up. Again, downloading the mags cures the problem for him.
He's just wondering if he wasted money on the McCormick mag, or if this is normal "new gun" teething.