Armscor Pistol Magazine, 40S&W/10MM, 16 Rounds, Fits Rock Island Ultra Full Size High Capacity Pistols, Steel, Blued Finish OEMP164015B This magazine is for Rock Island Ultra 1911 models chambered in 40 S&W or 10mm and holds 16 rounds of ammunition. It is made of steel and is made to Armscor/Rock Island Armory specifications and tolerances" using the same manufacturing and materials as the original equipment magazines" ensuring perfect fit and operation.