I'm afraid I can't be much help with the headspace situation. If the barrel has excessive headspace, you can return it. There is not much you can do personally without proper knowledge and lots of equipment. If the problem is that you don't trust your headspace gauges, return them to the maker and have them checked.
Building ARs has, in recent years, become a table top operation. If your intention is to build your own rifles, make sure your basic tools and hardware are of known quality.
Sorry that I cannot be of more help.
Bill Wylde