The present invention is directed to the field of firearms and more particularly involves an automatic/semi-automatic hand-held rifle of the type exemplified by the U.S. military M16.
The M-16 automatic rifle and the AR15 semi-automatic rifle have been the standard issue weapons of the U.S. military and civilian police departments for decades. The rifle design was originated by E. M. Stoner and developed by Fairchild Engine and Airplane Company in the 1950's. Modified versions of the M16 designated as the M16A1 and M16A2 are currently in use by armed forces in the U.S. and throughout the world. A civilian semi-automatic version of the M16 designated as the AR15 is sold to civilians by Olympic Arms of Olympia, Wash. When used herein, the phrase "M16" is intended to include all versions of the M16 and AR15 previously and currently being produced.
One of the basic patents on gas-operated firearms was that granted to Browning in 1938, U.S. Pat. No. 2,116,141, which was a divisional application of U.S. Pat. No. 2,093,705. These patents disclose a piston tube assembly for disengaging the barrel from the casing of the gun.
U.S. Pat. No. 2,951,424 issued to E. M. Stoner on Sep. 6, 1960, discloses the M16 bolt and bolt carrier system and the gas operation thereof. This patent discloses a rifle utilizing a gas tube that extends from gas ports in the barrel, back into the receiver of the rifle and into a gas tube pocket or "key" attached to the bolt carrier.
U.S. Pat. No. 3,198,076 to E. M. Stoner, issued Aug. 3, 1965, discloses a gas operated, magazine-fed rifle that can be readily converted to a belt-fed machine gun by inverting the barrel assembly.
U.S. Pat. No. 3,675,534, issued to P. C. Beretta on Jul. 11, 1972, discloses a gas-operated automatic rifle having a piston and stem inside a gas tube with the stem fixedly attached to the bolt carrier.
U.S. Pat. No. 4,358,986, issued to C. Giorgio on Nov. 16, 1982, discloses a gas-operated automatic rifle having a stationary piston and a segmented movable gas cylinder/operating rod assembly including a biasing spring.
U.S. Pat. No. 3,618,457, issued to A. Miller on Nov. 9, 1971, discloses a gas-operated rifle utilizing a gas-operated piston and rod assembly with the piston rod telescopically mounted over a stationary guide rod and being spring-biased.
U.S. Pat. No. 4,765,224, issued Aug. 23, 1988, to M. Morris discloses a modified M16 type of rifle utilizing an extended gas tube receiver on the bolt carrier which maintains telescopic engagement with the gas tube at all times during the firing cycle.
U.S. Pat. No. 4,475,438 to L. Sullivan, issued on Oct. 9, 1984, discloses an open-bolt gas-operated rifle with a short-stroke piston that kicks open the bolt carrier against a biasing spring, using a short-stroke piston movement.
While the aforementioned gas-operated rifles all disclose various means of actuating a bolt in an an automatic or semi-automatic rifle, none of these teaches a design for an M16 type of rifle that allows the rifle to be chambered for short pistol-type cartridges such as the 10 mm cartridge and the 45 caliber ACP cartridge. There is insufficient gas generated in the short fat pistol cartridge to fully activate the bolt carriers in these designs. Normal operating gas pressures generated with most rifle cartridges are in the 50,000 to 55,000 CUP range, whereas in the short wide pistol cartidges the pressures generated are in the 40,000 CUP range.
Because of these low pressures, automatic and semi-automatic weapons designed for short pistol cartridges normally utilize the "blowback" type of operation wherein the rearward force on the cartridge case from the burning propellant charge therein is utilized to drive the bolt backward in the receiver in order to eject the spent cartridge and chamber another live round.
The disadvantage of blowback type of operation is the gas backblast from the chamber area that tends to hit the operator in the face and cause discomfort and inaccuracy. Also, in situations such as military and police operations it is essential to be able to place suppressors or silencers on the muzzles of the weapons to suppress the retort from firing. Suppressors and silencers are ineffective on blowback types of weapons because of the sound escaping through the breech upon blowback of the bolt. Thus, a gas-operated weapon is required when suppressed firing is desired.
Another disadvantage of the blowback system is the problem of cartridge separation. If you have a weakened cartridge or one with a thin spot in the wall, or if you have an overloaded cartridge or one with higher than normal gas pressures, because of the nature of the blowback system the cartridge will separate, blow apart, or rupture. This is due to the combination of the cartridge defect or the higher gas pressure, plus the fact that the bolt in a blowback system does not lock-up in the breech.
When a cartridge does blow apart, separate, or rupture in a blowback system it creates a dangerous situation for the operator of the rifle and anyone standing near the rifle since gas and particles of the cartridge will be expelled backward and outward from the chamber. Another problem is in removing the upper end of the cartridge from the chamber since there is no rimmed end left for the extractor to grip nor any part of the cartridge projecting out of the chamber to be manually gripped and removed. A difficult and lengthy operation utilizing a broken cartridge extractor is required.
Also, in a fully automatic weapon or in a semi-automatic weapon being fired rapidly, the broken cartridge in the chamber will cause a bad and potentially dangerous jam when the next live round is attempted to be loaded.
One disadvantage of the gas-operated M16 currently being manufactured is the fouling of the gas ports in the bolt carrier and the gas rings on the piston end of the bolt. A large amount of residue from the burning powder collects in these small and rather tortured ports and grooves. Also, dirt and moisture from the atmosphere are mixed with the gas from the burning powder in the gas system and residuals are formed in the ports, and in the gas rings on the bolt, which eventually clog and jam the weapon. Gas exiting the ports from the bolt also mix with dirt and moisture and cause deposits between the bolt, the chamber, and the receiver, thereby interfering with proper operation of the bolt and bolt carrier in the receiver.