Last month, the folks over at Genesis Arms released the Gen-12 AR-10 12-gauge conversion upper. A 12-gauge AR? You got that right. Basically, this thing mates to a standard DPMS Gen 1 pattern .308 lower. Here’s a blurb on the upper, as well as a list of features, found on the official product page:
The 10 Best Accessories to Make Your .308 AR Great Again
Genesis Gen-12 Upper
The GEN12 upper will work with either the shorter DPMS buffer tube or the longer Armalite AR10/ 308 tubes. The center of the upper is the short recoil system which cycles the action, so there is no gas tube or piston. The cyclic rate can be tuned by adjusting buffer weights and springs by the end user.
The upper will reliably feed both 2 ¾” shells and 3” shells on a standard short DPMS 308 buffer and spring. It will cycle birdshot or magnums and most everything in between. This is sold as an upper so this does not require a FFL to purchase; however, you are responsible to know the laws in your state and purchase accordingly.