There was a company, I believe they were from Arizona, that short uppers for the AR-10. If my memory serves me correctly, they were 18". Back in 2015, I got a chance to talk to them at the Tulsa show. They moved on to making complete 50's that wouldn't destroy the lower. He said they made the first ones for the military over sea. They would get pinned down, and one soldier would pull the upper out of a back pack and take care of the problem. They then progressed to making an affordable 50. I haven't seen them or heard of them for a while now.