The 12.7mm M-16

LW15.499 (Leitner-Wise Rifle Company) mini-.50 caliber (12.7mm) rifle is based on  the M-16, but uses a shorter (thanthe standard .50 caliber) 12.7mm round. The mini-.50 rifles cost $1,450 to $2,250 each and weigh 6.3 pounds unloaded. The rifle is 36.2 inches long. Ammunition costs a 80 cents to five dollars a round (each one weighs about 1.1 ounces, with the most expensive ones being the armor piercing round). For a thousand bucks, you can get an upgrade kit for an AR-15 (the civilian version of the M-16). Fully loaded, with a ten round magazine, the weapon weighs about eight pounds.
While 6.8mm is the hot new rifle round being promoted for next-generation American  assault rifles, two companies are quietly promoting a "mini-50" .50 caliber (12.7mm) round as a supplement to currently rifle calibers. The mini-.50 would be used by special forces and law enforcement officers against re-enforced structures, vehicles, and advanced body armor. The U.S. Coast Guard has already bought a quantity of these weapons for use against "Go-fast" boats and some have reportedly appeared in Afghanistan.
To create the mini-.50, a .50 caliber bullet is put into a smaller casing (than the standard .50 round used in machine gun and long-range sniper rifles). The smaller casing trades off less propellant for softer recoil, less accuracy over longer distances, but less stress on the barrel and user. The recoil for the mini-.50 is described as being similar to a 12-gauge shotgun. It also makes for a weapon that is easier to carry and faster to employ than the full-sized .50 caliber rifle designs. The Barrett Light .50 M82A1 rifle employed by the U.S. Army and Marines weighs in at 28 lbs unloaded and is 57 inches long while a mini-50 weighs in at around 8-12 lbs loaded and a little over 36 inches long.
Like various 6.8mm projects, gun designers built a hybrid rifle using AR-15/M-16 designs to provide some compatibility with existing hardware. For example, a 30 round M-16 magazine will hold 12 of the fat mini-50 rounds. Conversion kits are available,  for around $1600.
each,  to convert an M-16 type rifle into one firing the mini-.50.
Portability and round penetration of the mini-50 family are the key traits to this weapons family. Armored glass that resists 7.62mm fire, yields to the mini-.50, as do doors, locks, and cinder blocks, and engine blocks. Since the rifle is only slightly longer and heavier than a 5.56mm design, it can be used in close range combat and other rapid fire encounters. Two Virginia companies are currently making mini-.50s, the Leitner-Wise Rifle Company in Alexandria (a stone's throw away from the Pentagon) and Alexander Arms, on space leased from Radford Arsenal. – Doug Mohney
LW15.499 (Leitner-Wise Rifle Company) mini-.50 caliber (12.7mm) rifle is based on  the M-16, but uses a shorter (thanthe standard .50 caliber) 12.7mm round. The mini-.50 rifles cost $1,450 to $2,250 each and weigh 6.3 pounds unloaded. The rifle is 36.2 inches long. Ammunition costs a 80 cents to five dollars a round (each one weighs about 1.1 ounces, with the most expensive ones being the armor piercing round). For a thousand bucks, you can get an upgrade kit for an AR-15 (the civilian version of the M-16). Fully loaded, with a ten round magazine, the weapon weighs about eight pounds.
While 6.8mm is the hot new rifle round being promoted for next-generation American  assault rifles, two companies are quietly promoting a "mini-50" .50 caliber (12.7mm) round as a supplement to currently rifle calibers. The mini-.50 would be used by special forces and law enforcement officers against re-enforced structures, vehicles, and advanced body armor. The U.S. Coast Guard has already bought a quantity of these weapons for use against "Go-fast" boats and some have reportedly appeared in Afghanistan.
To create the mini-.50, a .50 caliber bullet is put into a smaller casing (than the standard .50 round used in machine gun and long-range sniper rifles). The smaller casing trades off less propellant for softer recoil, less accuracy over longer distances, but less stress on the barrel and user. The recoil for the mini-.50 is described as being similar to a 12-gauge shotgun. It also makes for a weapon that is easier to carry and faster to employ than the full-sized .50 caliber rifle designs. The Barrett Light .50 M82A1 rifle employed by the U.S. Army and Marines weighs in at 28 lbs unloaded and is 57 inches long while a mini-50 weighs in at around 8-12 lbs loaded and a little over 36 inches long.
Like various 6.8mm projects, gun designers built a hybrid rifle using AR-15/M-16 designs to provide some compatibility with existing hardware. For example, a 30 round M-16 magazine will hold 12 of the fat mini-50 rounds. Conversion kits are available,  for around $1600.
each,  to convert an M-16 type rifle into one firing the mini-.50.
Portability and round penetration of the mini-50 family are the key traits to this weapons family. Armored glass that resists 7.62mm fire, yields to the mini-.50, as do doors, locks, and cinder blocks, and engine blocks. Since the rifle is only slightly longer and heavier than a 5.56mm design, it can be used in close range combat and other rapid fire encounters. Two Virginia companies are currently making mini-.50s, the Leitner-Wise Rifle Company in Alexandria (a stone's throw away from the Pentagon) and Alexander Arms, on space leased from Radford Arsenal. – Doug Mohney