Been thinking about a pistol-caliber carbine, but didn’t want to have to buy a whole new gun? With CMMG’s 9 mm upper receiver and AR-15-based 9 mm magazines, you can keep your favorite lower.https://www.shootingillustrated.com/articles/2020/3/4/range-review-cmmg-resolute-9-mm-upper-and-magazine-inserts/