Ditto on this question. It looks like the magazine for an M&P 15-22. Can you run those in a standard AR lower?
Ooh, maybe using one of these?
Better-Mag S&W® .22 Rimfire Magazine Adaptor - Redi-Mag
BACK IN STOCK. ORDER YOURS NOW!!! An innovative, yet inexpensive adaptor allowing the use of Smith & Wesson .22 Rimfire magazines in a standard AR15 lower receiver.www.redi-mag.com
There are also these, but I don’t know if they work well.
Catch22 S&W 15-22 Magazine Adapter for Standard AR Lower - (Stick on)
With the 15-22 magazine adapters, the S&W 15-22 magazine will work great with the Catch22 to provide true last-round-hold-open functionality.
www.righttobear.com
Catch22 S&W 15-22 Magazine Adapter for Standard AR Lower - (Clip on)
With the 15-22 magazine adapters, the S&W 15-22 magazine will work great with the Catch22 to provide true last-round-hold-open functionality.
www.righttobear.com