So I know you all see a million types of cycling problems here, but I'm really stuck and not really sure where to turn. Here's the back story...

Built my first lower on my own, and bought a complete upper off of an auction site. After taking the gun to the range, I run into a slew of misfires. Mostly stovepipes. After 40 or so rounds, I started getting much more consistency, and by the end I had no problems. When I took the gun apart, I noticed that the gas key was extremely loose. I took the BCG to my local gun store where the guy re-tightened the screws and applied some loc-tite to keep the screws from backing out.

Hoping that this would do the trick, I went and shot today. The problems seemed to be worse today, and I am at a loss as to what I should do.  

Here are some (what I think to be pertinent) facts:

-Stag Lower
-Spike's Upper with a generic "Mil-Spec" BCG
-Generic "Mil-Spec Buffer tube
-Ammo is 55 grain American eagle crap ammo
-Carbine Length
-What else may help?

Thanks for the advice. I should have a new B/C coming from the guy I bought the upper from.

One question I have, is that on the original B/C the gas keys were clearly staked. How could the key get loose if they are?

The usual cause is the screws are not tightened up enough or they break.
The screws may not be mil-spec.
Grade 8 or equivalent screws tightened to 50 – 58 in/lbs and staked.

I replaced the BCG to a matching brand group, and gun will still not cycle properly. I found out that the previous BCG not only had a loose gas key, but also too much headspace.

Not really sure where to go. Tried different ammo, BCG, etc.  Anyone else have any ideas?

Could it be possible that the spring isn't worn in enough?

pull your charging handle all the way back until it stops with port cover open. hold it there and look and see if you can see the bolt just past the port opening. is it behind opening or is the bolt visible in opening. it should be visible about a 1/16 to an 1/8 of an inch. make sure you pull charging handle until it bottoms out and hold it there and then look.