I am a bit confused on your recommendations for magazines for AR-15 s. I don’t own an AR yet, but have been buying some magazines (30 round) from the manufacturer I have chosen to buy my AR from (Stag Arms). My question is this: would it be unwise to invest in mags such as Tapco or the Magpul brands? What do you mean by purchasing OEM  mags? can these be from any AR manufacturer, even ones that are different from my AR manufacturer? Please clarify your thoughts on OEM versus aftermarket (e.g. Brownell’s, Tapco, Magpul, etc.).
Thanks a lot for your amazing blog! – J.B. from Michigan
JWR Replies: For most guns, I generally recommend buying only original government issue magazines, or factory original magazines. As I mentioned in several of my FAQs on firearms magazines, I consider most brands of aftermarket magazines little more than unreliable junk. Many of these have either dimensional problems (due to poor quality control), or insufficient heat treating of their feed lips. Both of these issue make these mags prone to jamming. You should avoid any magazines that are listed in mail order catalogs or online as “afterrmarket”, “commercial”, “G.I. type“, or “generic”.There are, however, some exceptions to this rule for AR-15 magazines that are made to full military specifications, and some brands or polymer magazines.
The makers to avoid include Triple K and the “USA” brand. This includes most of the steel M16 magazines on the market with the notable exceptions of SA80 magazines, HK steel (“Maritime finish”), and Sterling (England) steel magazines. (The Sterling mags work in both AR-180s and AR-15s.)
Some polymer magazines that do work well are Thermold, Beta (CMAG double snail drum) Orlite, and MagPul. (The latter makes the much-touted and incredibly robust  PMAGs)
Most of the USGI contract alloy magazines are trustworthy, with the exception of Cooper Industries and some of the early (with black follower) DSI/Sanchez 30 rounders. For further details on M16 and AR-15 magazines, see my M16 Magazine FAQ . The “mil-spec” magazines sold by Brownell’s work fine, because they are sourced from a military contract manufacturer that has genuine mil-spec tooling and employs proper quality control.