You are going to build a barrel? Well we know you can grow some good weed for sure. You should do a Youtube on why you should not smoke dope.
LOL! You win the interwebs today.
According to the ATF, the “weapon” is the lower, not the barrel. Those can be purchased, shipped and do not require a background check. In other words, they are not tracked by the feds.
You may lack faith in yourself, but should not underestimate others. There is no magic in the process, just appropriate tools and some skill. Excellent barrels were made in the 1700's with lesser tools than mine.
Gotta build a forge first though.
Then it will be a true M-4gery.