re: AR Upper/Lower Kit Brands

What barrel length upper did you get for the 7.62? I recently bought a complete lower that was categorized as "other", so trying to figure out what I'm going to do with it and thought about 7.62 since I seem to be able to find 7.62 ammo everywhere now. I recently finished building a 300 blackout pistol with a Bear Creek 10.5 upper on it and sort of want to do another pistol build. Not sure if 7.62 is any good in a pistol barrel or not. 350 Legend also caught my attention.