Was talking to a friend today and he was telling me that it is possible to build a complete AR buy just buying the parts and machining and drilling some parts and not having to have a serial numbered fire controlled part. I don't know anything about AR's but I think this is not Correct. Your opinion would be appreciated.

W, Bill

Your friend is correct. You can do the same thing with 1911's and Glocks and the 10/22.
Just be sure you are making your own, and he's not making it for you, or vise versa.

You can buy an 80% machined lower, and finish the drilling etc yourself. So this would be a personal firearm, and does not need to be registered. You can not make these completed units for sale, the intent is self use.
No other part is tracked.
An 80% lower cost about the same as many completed lowers like an Anderson, but they are on the books.

https://duckduckgo.com/?q=80%25+lowers&t=ffnt&atb=v141-6__&ia=web

Really? So a serial numberless ar is legal?

yes

Thanks guys

You can make any firearm for yourself with no numbers, so long as it does not violate some other provision of the firearms laws such as being fully automatic or a short barreled rifle/shotgun.

Just takes a couple pipes to make a slide fire 12 gauge.

However, I don't believe it can be sold without a serial number - can somebody check me on that?

Yes, same as any other non-NFA firearm. It's not anything peculiar to ARs.

It can be sold, be you can't be in the business of selling them.