I have a 2 questions:
I thought if you build an AR rifle from parts you could not sale it as a complete rifle, that you could only sale as parts.
Second, I live in Texas but do not have a CHL, can I load my RIFLE mags at home and transport them to the range loaded, not with a mag in the rifle just pre-load my mags.
A lower receiver is the ONLY part that is restricted. If you buy a lower and then add an upper to it (making a complete weapon) you can sell it however you like.
As far as transporting loaded mags with a weapon in the same vehicle, that might not be a good idea (depends on your State). Your best bet is to always keep the weapon and ammo seperate and just load mags when you get to the range.
C4
Isn’t there an 11% federal excise tax that has to be collected and paid to Treasury on sale of the now complete rifle? Or is that “infringing”? 
The person that pushes the pins in (the first time) is responsible for paying the 11% FET. I am about 100% certain that most nobody does this.
C4
Disclaimer: I say this more as a question, not as a statement of fact, but…
Wouldn’t the problems with resale only crop up if you had machined the lower yourself, from one of those 80% forgings?
But isn’t that just for a “manufacturer” and not you average Joe who puts together a rifle, decides he doesn’t like it and the sells it ?
Mike
Personal Use. FAET does not attach in cases where a manufacturer, importer or producer incidentally manufactures, produces or imports a taxable article for personal use. See 27 CFR Section 53.112(b).