Low prices on the Rock River Varmint A4 .308WIN start at Champion Firearms: Unlike other major AR-10 manufacturers, Rock River Arms does not build rifles in an assembly line process. Instead a skilled armorer is dedicated to building strictly the lower assembly and another armorer the upper assembly. After the upper and lower assemblies are completed, they are then fitted together by yet another armorer.
Every major component of a Rock River AR10 starts out as either bar stock or a forging. Upper and lower receivers are made from forged and milled mil-spec 7075 T6 aluminum alloy that is then hard anodized to a surface hardness of 70 on the Rockwell scale. All components are held to extremely tight tolerances to ensure maximum accuracy. After final machining, each receiver is carefully polished to remove dings, scratches, and other small imperfections left over from the forging and milling processes.
Once polished to a perfect mirror sheen, the receivers are then sandblasted and sent out for anodizing. This polishing step is unique, and is why minor receiver imperfections, such as those normally found in front of the magazine well, are not encountered on Rock River rifles. Smaller parts, like the bolt stop, safety, and trigger components are investment castings made from 8620 steel that are case hardened to between 89 and 92 Rockwell.
After installation, the barrel's feed ramp is highly polished and contoured into the upper receiver, thus eliminating the common "step" between the barrel extension's feed ramp and the upper receiver that is found on most AR-10's. As a result, Rock River rifles enjoy significantly improved reliability with all types of 308WIN ammunition. Once the rifle is fitted, the barrel is lapped and additional touches made to ensure superior workmanship, accuracy and quality set all Rock River apart from other AR-10 manufacturers.