This article is an excerpt from the Gun Digest Book of Classic Combat Rifles.
Military surgeons all over the world have asked the United Nations to ban small caliber high-velocity rounds in combat — including the 5.56×45mm and the 5.45×39mm cartridges — which they believe cause unnecessary pain and suffering.
Switzerland re-designed the M855/SS109 round with a thicker jacket to stop fragmentation upon impact.
This new cartridge, however, was significantly more accurate at longer ranges than the M193 Ball cartridge, boosting the maximum effective range to 800 meters. To accommodate this new cartridge, a new barrel twist — from 1:12 inches to 1:7 inches — was required to stabilize the heavier 62-grain bullet.
There was a catch: the SS109 ammunition could not be fired accurately in an M16/M16A1 rifle due to its slower rifling twist. The bullet would not stabilize and would “keyhole” in flight. This new cartridge was about to be adopted as the M855 Ball cartridge of the U.S. military and the new PIP project would redesign the M16A1 rifle around this cartridge.
The United States Marine Corps began negotiations with Colt in January of 1980, asking for three modified rifles that would make use of the new FN SS109/XM855 cartridge and would incorporate four Marine-designated changes:
1. The sights must be adjustable to 800 meters.
2. The bullet must be accurate to 800 meters and possess the capability to penetrate all known steel helmets and body armor at 800 meters.
3. The strength of the plastic stock, pistol grip and handguards — as well as the strength of the exposed portion of the barrel — must be improved.
4. The rifle must have the full-auto capability replaced with a 3-shot burst mode.
The Joint Services Small Arms Program (JSSAP) PIP
The first rifles arrived from Colt in November of 1981. The USMC Firepower Division at Quantico, Virginia, would lead the PIP project. On November 11th, 20 Marines and 10 soldiers from the 197th Infantry Brigade at Fort Benning, Georgia, would take 30 M16A1 rifles and 30 M16A1E1 (PIP rifles) and test them for a month.
The test report was issued on December 11th and the conclusions were as follows:
• The sights were easily adjusted in the field by hand rather than with a bullet tip.
• Increased the effectiveness at long range, more so than the M16A1.
• More durable plastic furniture on the M16A1E1, for hand-to-hand combat.
• Sights were better for low-light conditions thanks to a larger-diameter (5mm) close-range aperture in the rear sight.
• Increased ammunition conservation and more effective fire with the 3-round burst than with full-auto fire.
• Utilized the XM855 NATO (SS109) ammunition, which improves the accuracy and penetration at all ranges. The product-improvement (PIP) “M16A1E1” was classified as the M16A2 in September of 1982 and was adopted by the United States Marine Corps in November of 1983. The Marines ordered 76,000 M16A2 rifles from Colt. The Army did not adopt the M16A2 until 1986.