A modular rifle family from my Macross Alexandria fanfic universe:
Saint Barbara Arsenal K2065:
The K2065 is an assault rifle/carbine in service in the Alexandrian Union Armed Forces. It fires a 6.5x45 mm caseless telescoped (CLT) cartridge and feeds from a 30 round polymer box magazine or a 60 round drum magazine. The K2065 uses a long-stroke gas piston operating mechanism, and the bolt carrier assembly is coated in a self-lubricating electroless nickel-PTFE finish for maximum reliability even in extreme conditions. The K2065 is available in several variants which include, aside from the standard rifles and carbines, a CQB version with a 265 mm barrel, a designated marksman version with a 457 mm barrel and a infantry automatic rifle version with a fluted 420 mm barrel. The K2065 is part of a family of firearms that share a common trigger module with select-fire (safe-semi-3 round burst-auto) or semi-automatic (safe-semi) trigger mechanisms available. Stocks are also interchangeable, as well as pistol grips. This family includes the SG2065 shotgun and the MP2065 personal defense weapon. All firearms in this family have a Picatinny rail in the 12 o'clock position for mounting optics and KeyMod slots on the 3, 6 and 9 o'clock positions for mounting other accessories.