Stick with any USGI mags and you will be ok. I believe that Cooper's are fine as long as they have the 6 spot welds on them. Colt mags are equivalent to the USGI mags they just seem to be overpriced because of the Colt name. Thermold's made in the USA are also good, 2nd tier, mags, and Israeli Orilites are behind them. What ever you do stay away from steel ar15 mags. Also, there is a brand name of ar15 mags called USA. Stay away from them because they suck ass and only made enough that actually worked to keep selling some to unsuspecting people.