New to the AR? Need help with your first purchase? READ HERE FIRST!!

[hals1]

I picked up a Bushmaster M4 from an individual (no trail). I then found this site and found it is not as great a gun as the hype. Anyway, it's a 16" and I really wanted a 20" so I ordered a BCM upper, BCG and YHM handguard for it. I also have a CMMG .22 conversion kit.
I was thinking of making the Bushmaster upper a more or less dedicated .22 and using the BCM for 5.56.
Then I got to thinking, why not get another lower? I will pick one up off the books so it will be a target of opportunity.
I need to know what to look for in a lower (stripped or complete) and what to avoid.
I'm in Wyoming (a Sarah Brady "D" state) so configuration is not a problem, as long as it isn't NFA.
Any advice?

Thanks,
Hals1