The .221-17 IMP was an experimental military cartridge developed under contract by Remington in the early 1970s for use in the Colt IMP carbine.
2,500 rounds were manufactured, a number of which having been fired in the testing of the IMP.
Design Details[]
Based on the .221 Remington Fireball cartridge, the .221-17 IMP was designed to provide a lighter munition with a higher muzzle velocity.
As a means of reducing weight, the cartridge casing is made of a composite of a nylon plastic body with a multi-piece steel base. To achieve that higher muzzle velocity, the cartridge uses a sub-caliber .17" diameter projectile encased in a six-petal, .221 caliber plastic sabot.
The projectile weighs 24.8 grains (1.6g) and measures 13.4mm (.528 in) in length. The plastic sabot weighs 2 grains (.129 g) and measures 9.906mm (.390 in) in length.
The cartridge uses a small rifle primer that is nickel-plated.
The 2,500 rounds produced by Remington were packed in red, green, and white 20-round cartons.