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The AR-17HMR upper is a gas operated direct impingement delayed blowback system. Patent pending. It is designed to prevent the firing pin from making contact with the cartridge unless it is locked in battery. I will explain why this is important.
Early on when the 17 HMR cartridge first appeared everyone was chambering rifles for the new hot round, including semi-automatic blowback designs by the major manufacturers. What they found was many people treated it as they would a .22 rimfire and not clean or maintain the rifle. What would happen was, on semi-automatics, eventually the bolt wouldn't close all the way and a round would fire out of battery with catastrophic case failure. Ours prevents the firing pin from making contact with the cartridge unless safely locked in battery and will not fire- until you clean it.
Another problem with blowback actions and the 17 HMR is the pressure on such a small bottleneck round varies enough to make balancing the bolt mass and recoil spring difficult. We leave ours locked until the pressure is reduced which allows us to use a much lighter bolt. A lighter bolt reduces the amount your sight picture jumps around during recoil. Also, accuracy is improved, as the system is locked during firing.
We use a stainless steel barrel just like competitive marksmen use to improve the useful life of the barrel; as we expect them to be shot a lot. The muzzle is threaded for flash hiders muzzle brakes and suppressors.
We use Black Dog Machine magazines. They are reasonably priced and plentiful. The magazines are made of Polycarbonate plastic with Nylon feed lips and are good for thousands of rounds. We are in California and to avoid any legal issues only ship 10 round magazines. Black Dog Machine sells 14 rounders if you are in a location where you are able to buy them. I am working on Kevin to make a 30 round magazine. He may if there is enough interest. (wink)
Be sure and pay attention to how to change out your buffer system. And watch out for the roller locker balls when you remove the bolt. They are not caged and will fly out and run under something big and unmovable. Also, you need to depress the gas key and retract the rollers to install the bolt back into the upper.
We are operating out of a small shop right now to keep our overhead low. However, the upper is designed with a minimum of parts that are relatively easy to manufacture. And the inherent design is easy to manufacture in quantity.