Zastava M21
The Zastava M21 is a series of 5.56×45mm NATO rifles developed and manufactured by Zastava Arms in Serbia. Description. The M21 is based on the Kalashnikov rifle, chambered in the 5.56×45mm NATO cartridge. The current models use a 1.5mm thick stamped receiver, while a future model will feature an improved receiver of 0.9mm thickness to achieve a considerably lighter weight. Like many modern assault rifles, the M21 can incorporate picatinny rails for mounting accessories like optics, vertical grips, bipods, etc. The Zastava M21 is gas operated, long stroke piston with a rotating bolt locking  system rifle. It features a hard chromium-plated, cold forged standard rifled or an optional polygonal rifled barrel, integrated 22mm flash hider grenade launcher, heavy-duty synthetic furniture with a polymer folding stock similiarly to the AK-74M, and side optics rail as standard (optional adapter base for cover mounted picatinny rail also available). The rifle can also mount a 40mm under-barrel grenade launcher. It has a magazine capacity of 30 rounds. The cyclic rate of fire is 680 rounds per minute, and the sustained rate of fire is 120 rounds/min. The Zastava M21 uses a  conventional barrel, while the Zastava M21B uses a polygonal barrel. The regular barrel has six grooves with a right-hand twist. An octagonal polygonal version is also available and has four grooves with a right-hand twist (M21B). Barrels are also hard chrome plated to provide a longer service life. The rifle has conventional iron sights that consist of a front post and a flip-up rear sight with 300m and 500m apertures. However, much like the RK 62 and IMI Galil, the front and rear sight have been relocated to the gas block and top cover respectably . It also borrowed the Galil's thumb safety. The top cover is hinged like the AKS-74U. A set of picatinny rails on the hand guard can mount various optoelectronic devices. The M21 is a modular weapon, with configuration dependent on the task and mission. Choices of optical sights include "TELEOPTIK" (ON M04) and "ZRAK" (ON M04A). Optoelectronic devices include a reflex sight ("MARS" M04), two bookmark target lasers ("AIM2000" M04A and "INFIZ" M04), two passive monoculars (M04 MINI N/SEAS and "MARS" M04+MINI N/SEAS), passive sight ("SOVA" PN 3x50). Variants. The M21 comes in several assault rifle and carbine  variants: