User:Casperthelazyghost/sandbox

While a plethora of methods of unique gas operation and recoil operation existed in military small arms nearly 50 years ago, many of these systems have been ditched for gas operation. Recoil operation has more or less disappeared entirely from rifle design. The HKG36, FN-SCAR and other successor designs to the FN FAL and CETME(the most widely used recoil operated small arms)have ditched their recoil operation for the short stroke gas piston. Instead the successors to those rifles utilize the Sudayev-Stoner gas system found in the AR-18. The last serious holdout in this regard is the AR-15. Whose pseudo direct impingement gas system utilizes the Bolt Carrier Group as a gas piston rather than impinging directing onto the face of the BCG as conventional direct impingement designs do.

Since the release of the AR-18, self-loading intermediate caliber rifles have converged toward three popular operating systems. These exist today as Kalashnikov long stroke gas piston derived designs, derivatives of the AR-15 and the Sudayev-Stoner gas system found in the AR-18 rifle. Excluding the United States and former member states of the Warsaw Pact, nearly every nation uses a design derived from the AR-18. In some cases, designs borrow more than just the AR-18's gas system. The HOWA Type 89, Singapore SAR-88 and Taiwanese T-91 are either modernized AR-18s or utilize a complete AR-18 upper receiver. The British L85 is little more than an AR-18 in bullpup configuration. In fact, some L85 prototypes were AR-18 upper receivers mated to a prototype stamped metal bullpup lower receiver.

Rifles which borrow the AR-18 gas system include: HKG36, HK416, HK433, FN-SCAR, Steyr AUG, CZ 805 BREN, Chinese QBZ-95 and Daewoo K2 in addition to Type 89, SAR-88, T-91 and L85. These rifles are the standard issue arms of X countries, making the AR-18 Sudayev-Stoner gas system the second most popular method of gas operation behind the AK- long stroke gas piston. However it is worth noting that while over 50 million kalashnikovs have been produced, there have not been many non-Warsaw pact countries to adopt the Kalashnikov long stroke gas piston. A notable exception is Switzerland, whose SG-550 uses the Kalashnikov operating system.