I had a Ciener drop in bolt replacement from Midway. Ran like shit until I fed it Federal Bulk Pack from Walmart. Ran like a TOP! I used it for a combative carbine class and had zero, yes ZERO issues, whereas plenty of people shooting Sigs, .223 ARs (one with an M&P had a stuck case), and even AKs were having trouble.

It hated Minimags, but absolutely loved the Federal cheap stuff.

I also had to clip a couple coils off the recoil spring. It would occasionally double fire before I did that.

Oh and +1 for Black Dog mags, worked great for me.

Edit: Whats the "ball detent" mod?