For those looking to build an AR-15 rifle that is different from your standard direct impingement style, Primary Weapon Systems has you covered. The PWS MK116 Pro Complete Upper Receiver features a 3-position adjustable long stroke gas piston system for the ultimate in reliability and smooth function. The gas block adjustment switch is easily accessible through the free float Pic-Lok handguard, so you can quickly add picatinny rails or M-LOK accessories. The barrel is machined from 416R stainless steel and features a .223 Wylde chamber for extreme accuracy potential. Additionally, the 16" barrel is button rifled with a 1:8 twist rate and comes with an A2 style flash hider. Change up your AR collection with the PWS MK116 Pro Piston Upper.Features: 3 Position adjustable long stroke gas piston Mid-Length piston system 16" barrel chambered in .223 Wylde 416R stainless steel and Nitride finished A2 flash hider Button rifled 1:8 twist rate Proprietary slick side upper and BCG Forged 6061-T6 aluminum Radian Raptor charging handle Pic-Lok free float handguard Weight: 4 lbs. 14 oz.The proprietary piston upper receiver is forged from 6061 aluminum and features a slick side design with an M4 flat top Picatinny rail for easily mounting optics. Even though it uses a proprietary upper and bolt carrier group, it is still compatible with AR-15 charging handles like the ambidextrous Radian Raptor.The mission at Primary Weapons Systems is to provide the highest quality tactical and sporting rifles and accessories for sportsmen, military, and law enforcement at a fair, competitive price.