manufactured in Northern Ireland with "Round Sections" (Round shaped receivers) and "Square Sections" (Square shaped receivers), the Avenger submachine gun which was used by Loyalist Paramilitaries was considered one of the best designs for its type. The bolts were telescoping with a forward recoil/return spring with in the rear, a heavy coil spring that acts as a buffer increasing accuracy and recoil handling. The barrels were usually found lacking rifling but this can in some cases possibly increase ballistics at close quarters. It used Sten magazines and had the capabilities of adapting suppressors. During the 1970s–80s, International Ordnance Group of San Antonio, Texas released the MP2 machine pistol. It was intended as a more compact alternative to the British Sten gun (although in its components and overall design have nothing directly similar to the STEN), to be used in urban guerrilla actions, to be manufactured cheaply and/or in less-than-well-equipped workshops and distributed to "friendly" undercover forces. Much like the previously mentioned FP-45 "Liberator" pistol of World War 2, it could be discarded during an escape with no substantial loss for the force's arsenal. The MP2 is a blowback-operated weapon that fires from an open bolt with an extremely high rate of fire. A more common weapon of Guatemalan origin is the SM-9. Another example is the Métral submachine gun designed by Gerard Métral intended for manufacture during occupation and undercover circumstances. A unique example is the Soviet S4M pistol, designed to be used expressly for the purpose of assassination. It was a simple break-open, two-shot derringer, but the unique features came from its specialized ammunition, designed around a cut-down version of the 7.62mm rounds used in the Soviet AK-47. The casings of the round contained a piston-like plunger between the bullet and the powder that would move forward inside the casing when fired. The piston would push the round down the barrel and plug the end of the casing, completely sealing off any explosive gases in the casing. This, combined with the inherently low-velocity round resulted in a truly silent pistol. The nature of the gun and ammunition led to it being wildly inaccurate outside of point-blank range. To add further confusion and throw possible suspicion away from the assassin, the barrel rifling was designed to affect the bullet in such a way that ballistics experts would not only conclude that the round was fired from an AK-47, but that