This is our M10 side cocking upper receiver. It will come with either 1/4" (shown) or 1/2" 1913 Picatinney  rail. There will be a $25.00 charge for the 1/4 rail due to additional machine time.  It is entirely made of steel and has an adjustable front sight.  The cocking handle is nonreciprocating and spring loaded.  The upper is parkerized which is the traditional finish of the MAC series of guns. Barrel options for 9mm are: The standard barrel threaded 3/4-10, the stubby barrel threaded 1/2-28 or the double threaded 3/4-10 and 1/2-28.   Barrel options for the 45acp are: The standard barrel threaded 7/8-9, the stubby barrel threaded 5/8-24 or .587-28 or the double threaded barrel threaded 7/8-9 and 5/8-24 or .578-28. They are pinned in place and made of CrMoV MIL-B-11595 material with 6 – groove, 1:10 twist and precision air gauged with inert gas vacuum stress relieved after button rifling process. The finishing is manganese phosphate, the traditional dark gray/almost black parkerizing of the MAC series guns . These were profiled on centers to provide accuracy between bore and profile which has been a problem we’ve experienced with other manufacturers’ barrels in the past. This item is a custom order item, please allow at least two weeks for shipping. Note:  Lower receiver and bolt assembly not included.  If this upper receiver will be used on an early M10/45 with a bolt using a pin style extractor,  please let us know if the comments section upon checkout so that we can relieve the barrel for the extractor.  If you select a 9mm barrel with 1/2-28 threads, we do NOT recommend shooting this barrel in full auto with the 1/2-28 threads exposed due to the thinness of the barrel wall at the 1/2-28 threads.  Repeated firing with exposed threads may cause the barrel wall to weaken and/or split.  We recommend always using shooting this barrel with a barrel accessory, such as a thread protector, flash hider, or suppressor firmly secured to the end of the barrel.