History of the original M4 Survival Rifle
The M4 was developed from the Harrington & Richardson bolt-action M265 sporting rifle, adapted to a sheet metal frame with telescoping wire butt stock, a 14-inch detachable barrel chambered for 22 Hornet and the 4 shot detachable box magazine of the Savage Stevens M23D .22 Hornet sporting rifle. The M4 weighs approximately four pounds and with barrel detached and telescoping stock closed makes a ~14 inch overall package.
Due to the possible use of the M4 by downed aircrew as a combat weapon, military issue ammunition in .22 Hornet was loaded with full metal jacket bullets to comply with the Hague Convention barring use of expanding bullets in warfare. It was later determined by the USAF that exigent circumstances and self defense would have exempted soft point ammunition from that provision.
In the 1950s, the M4 was supplanted by the M6 Aircrew Survival Weapon and the M4 was phased out along with the decommissioning of the aircraft containing M4 as part of their survival package. The Armalite AR-5 (MA-1) was approved as a replacement for the M4 but no significant quantities of the AR5 were procured, as there were sufficient numbers of M4 and M6 in inventory to meet USAF needs.