That's a cheap and lazy assumption. I own an AR pistol that I had build and I had two bushies that I traded for my car.
That's great. I have 5 Rock rivers in various configurations, 3 of which I built myself. Not one of them jams.....ever. I've let them sit between 2-3 range sessions WITHOUT cleaning and they still have never jammed.
If yours are jaming then YOU didn't build it right.