I just purchased a PROMAG 32 RD, A Butler Creek 20 RD, an Eagle 30 Rd and a Ram Line 30 rd
I took them all to the range today:
PROMAG: Fit lose in the rifle, but fed fairly well. I went threw two magazines and it jammed once. I wouldn't trust my life to these but at the range it is nice not to spend half the day loading magazines (especially when you pay by the hour!) The magazine cost me $15.99. It is a plastic magazine with metal lips. Very easy to load.
The Eagle Magazines were horrible. I got them for $7.99 so figured they were worth trying. I had MULTIPLE jams, problems with the bolt catching on the magazine. I could have hand loaded a single shot faster than firing and clearing a jam with these magazine. I only shot two magazines and will probably never shoot it again. This is a completely plastic magazine.
The Butler Creek Magazine worked great. It fit nicely in the rifle, and I went thew three magazines without a jam. This magazine was given to me by a friend. He told me he has had decent luck with them. This is a plastic magazine with a rubber type lip. Easy to load.
The Ram Line is nice in size, it is half the length of the Promag. The bullets line up side by side instead of on top of each other. It jams. It jams quite a bit. It's pretty stiff to load. It wasn't as bad as the eagle but i wouldn't trust it to fire when I pull the trigger. I got this at a gun show for $10.00. All Plastic.
Keep in mind, I only had a half hour for lunch and only got to throw about 360 rounds of lead down range. I would take any of these magazine (minus the Eagle) to the range, but I would NOT use these in a situation where I needed them to work. Also note, I only got to fire each magazine a few times, but I am pretty sure magazines are much like wine. i don't think they get better with age.
The best magazine of course is the factory magazine that came with the rifle. I have shot hundreds of rounds, with all sorts of ammo, and it has NEVER jammed. It's only ten rounds, but i would trust it to fire when I pull the trigger. I am going to pick up a few more of these.