The Ruger 8506 stripped lower is the best lower ever. Seriously, the internal dimensions ensure uppers fit snug/tight so they don't freaking rattle. I always thought it was the upper that was the problem, but it's been lowers all along.

Also, the lower looks and feels like it was made by Mega.

In summary, take your upper to an FFL that has these in stock, verify it fits snug/tight, and buy it.