My first experience with Primary Weapon Systems (PWS) occurred shortly after it started selling complete upper receivers. At the time, much effort was being spent on finding a truly reliable piston-driven AR with a 10-inch barrel. In meeting with PWS’ representatives, I was immediately impressed by their honesty, a rare forthrightness in doing business. At the height of the piston craze, the marketing was thick. PWS just told me it would send an upper and gave me several officer contacts so I could get their impressions. After following up with them, one thing was clear: the uppers worked.
When the PWS upper arrived, it was put through one the most rigorous and thorough tests I had ever carried out. (There was little doubt these guys had the whole short-barreled piston-AR thing down.) After thousands of rounds, the upper never missed a beat. It is about as close as you get to AK-47 reliability in an AR.
Eventually it became more common to see these uppers at police department trainings and classes. At one training, a PWS Diablo (7-inch-barreled upper) was put through two days of dust, dirt and cold in the Nevada desert. The upper worked flawlessly too include hits at some pretty long range. Primaryweapons.com.