I always seem to have a project or three in the works. I think it depends how quickly I want to complete the project. If I really get the itch I'll borrow parts from other rifles.

I'm up to 6 completed rifles/SBR's right now and I may or may not SBR another lower that's just sitting in the safe. I don't like the idea of having a bunch of uppers and just one lower. Lowers are cheap...