Due to the severe large numbers of surplus of M14 magazines, Westrom found a way to make it happen. By purchasing M14 magazines and modifying them, every customer could have a rifle with a high capacity magazine that was in compliance with the Assault Weapon Ban, due to the fact the M14 magazines were all manufactured prior to September 1994. This went on through the sunset of the Assault Weapon Ban in 2004. Now Armalite was free to manufacture their own magazines.
Initial rifles stayed with the modifed M14 magazines, and now Armalite produced new magazines that were modified and functioned even better than the M14 magazines. However, there was an increased popularity of AR10 type designs from many other companies in the industry. They chose to go with the SR25 type magazines. There were multiple manufacturers of the SR25 type magazine, including Knights Armament Company, Magpul, C Products Defense, etc.
Due to customer demand, Westrom introduced the new AR-10A, which required modification of both upper and lower receivers to accept the SR25 pattern magazines. Since that time, Westrom has sold Armalite and the new company has chosen to discontinue use of the M14 type magazine in favor of full production of rifles utilizing the SR25 pattern magazine. So the AR-10A is now the standard model manufactured by Armalite. Armalite still provides modified M14 magazines, as well as the latter post-ban M14 based magazines to support existing customers. As a side note, the designer, Mark Westrom, felt then and feels now that the M14 type magazine is much stronger, more durable, and more reliable than the SR25 type magazines.