Colt AR-15 "SP-1", .223 cal. semi-auto rifle. Serial #SP98948 mfg. 1978. Excellent condition. The early civilian version of the Vietnam era M16 with triangular forearm, bayonet lug, no forward assist, hollow pistol grip, fixed buttstock, 20" skinny barrel. Excellent chrome bore, birdcage flash-hider and solid carry handle. This beauty is very clean with 98% parkerization.æ Vent forearm. Black web sling. These are quite collectible and this one is super nice. A must have for all Vietnam vets!