17/221 IMP

Research notes

In the late 1960’s the Air Force Armament Laboratory began work on an improved aircrew survival weapon designed to be lethal yet small and lightweight. Colt Industries was given a contract to develop a weapon using the ’stockless rifle’ concept. The result was the GUU-4/P Individual Multi-Purpose weapon - IMP for short. Colt made five IMPs chambered to fire the .221 Remington Fireball cartridge.

This version was designed to provide a lighter round with more velocity. Remington developed this cartridge under contract. Cartridge weight was reduced by making the case body from plastic and joining it to a multi-piece steel head. Greater velocity was obtained by using a .17 caliber bullet carried in a .221 caliber plastic sabot. Six slots in the sabot cause it to separate from the bullet on muzzle exit. Remington made 2500 of these rounds and packed them in red, white and green 20 round cartons.

NOMENCLATURE : .221/.17 Plastic Steel OVERALL LENGTH : 1.753" TOTAL WEIGHT : 84.4 gr BULLET SABOT PRIMER Type : full metal jacket Material : Clear plastic Type : Small rifle Diameter : .172" Diameter : .226" Material : Nickel plated Length : .528" Length : .390" Sealing Lacquer : none Weight : 24.8 gr Weight : 2.0 gr

CARTRIDGE CASE PROPELLANT Headstamp : none Type : Rolled ball Material : Blued steel (base) + mustard colored plastic (body) Weight : 17.0 gr Length : 1.395" Base Length : .264" Rim Diameter : .373" Shoulder Diameter : .355" Neck Diameter : .251" Weight : 40.7 gr (primed)