The 0940 upper is a dedicated AR-15 pistol caliber upper receiver assembly with an appropriately sized ejection port window. It is compatible with 9mm, .40 S&W, .357 SIG, 45acp and 10mm. Technical Specifications Compatible with 9mm, 40 S&W, 357 SIG, 45acp and 10mm Machined from 7075-T6 billet aluminum with a matte black hard-coat anodized finish Slick side upper receiver with pistol caliber sized ejection port and no forward assist or dust cover door Works with any mil-spec lower receiver Upper weight: 6.5 oz