Really 4.5 stars - Guntec USA AR-15 Stripped Billet Upper Receiver

I've used three of these upper receivers on builds, and, like any other upper receiver on the market, you have to pair these with the right lower receiver; some will be extremely tight and some will be a little bit sloppy, however, I've noticed some slight inconsistencies in the measurements of the pivot pin lugs, which can be easily corrected with a little bit of paint (I really like AlumaHyde - do it right and it comes out great).
I've found these to fit very well with Broken Arms (AKA Broken Armory), and Red Horse Arms, and Range Tool lower receivers (Note: this is where I discovered the slight inconsistencies with the machining of these uppers while testing fit with several brands lowers, yet easily fixed).
After putting on a coat of AlumaHyde on the one upper receiver that needed it, of the two uppers I bought, all play went away and it is about as tight a fit as you can dream for.
I very much wish I could post a photo with my review so you could see the fit I got with a Red Horse Arms lower receiver (hopefully Optics Planet will start carrying both of the aforementioned manufacturers' lower receivers.
I very much do recommend these for your billet builds (forged with billet just looks funny to me.