Buy USGI, they will work in any AR. The aftermarket brands, like USA and so on, don't work well in a lot of AR's. I have about 9 30rd Orlites for my Colt and have had no problems with functioning, however, Its hard for me to attest to their durability when I keep them stored in my safe. I hear Thermolds are a little bit better than Orlites but I have no experience with them. Buy some Colt-AR15 brand 20's with the aluminum follower, they are my favorite for shooting. You can find them used if you look for them. Hope this helps.