Its not a big trick to be enough of a mechanic to assemble an AR from parts.
Where the mechanic skills start to evolve into gunsmith skills includes standards,responsibilities,and a sense of doing things right.
I bought and returned an excessive headspace cut rifled barrel from an outfit that was known to have their uppers and rifles in the winners circle on a national level. They made things right without question,and I don't want to trash their reputation.I'd buy from them again.
But still,I KNOW I can spend near $400 for a top grade barrel and get one with excessive headspace because I have done it,and the reason I know is BECAUSE I CHECKED IT.
If you don't check them,you have no clue what friends and family are putting their face behind.
If a guy builds one AR without gauging it,well,maybe he isn't going to build more rifles. Maybe he doesn't need to buy gauges.
But at some point,there will be a local gunsmith or friend with gauges,and it can get checked.
When someone tells me "I built a hundred AR's and never checked headspace,what impresses me is that a set of headspace gauges would add about 70 cents to the cost of each rifle.
Like,the more you build,the less sense it makes to not have gauges.
If I can come up with a reamer for a wildcat,I can come up with a gauge.
I figure my rifles will be shooting after I'm dead,but the quality of my work will still be there.
Every rifle I build gets headspace checked.Nothing else will do.