This a 10-round factory Mossberg 715 magazine.
Mossberg is world renowned for their impeccable shotguns. They now have an AR-15 style .22LR rifle which is a variant of the Mossberg 702 Plinkster.
This magazine is a well-built polymer design that has the appearance and size of a full-sized AR-15 magazine. This magazine is a 10-round capacity in a full length 25rd body. These magazines are for use in restricted states.