The MWG 90 round magazine is seen by many as a less expensive alternative to the Beta C Mag. It is made of polycarbonate resin and has a rear window so that you can check on the remaining rounds. The MWG 90 holds a maximum of 90 rounds and can be stored virtually indefinitely with 80 rounds loaded. Test reports indicate that it is at least as reliable as a C Mag if not more so, but may be less robust. It is, however, guaranteed not to jam or mualfunction. Some shooters dislike the way the mag curls to the left rather than the right as it puts right-handed shooters at a disadvantage and means you really have to have a fore-grip positioned well forward on your rifle’s fore-end (you may also get mistaken for the Mall Ninja!). The MWG 90 is easy to load and comes with a 10 round loading chute and nine stripper clips to ease the loading process. The MWG 90 weighs 1lb. 4 oz (.56kg) wt. empty and takes .223/5.56X45 mm rounds.
Check the price of the MWG 90 round magazine at Brownells, a name you can trust.
You may find this introductory video on AR triggers interesting.