Remember, the ATF applies the "constructive possession" rule with most NFA items.
So, if you order up a 14.5" bbl with the intent of welding a flash hider on there permanently, but it comes from the shop/mail without such welding already done...
But you also own any compatible lower...
You've potentially committed a federal felony, even if you never mount the upper on the lower.
Either get your upper first and weld then get the lower if its your first AR, or have the flash hider permanently welded on there before you take possession of the upper, or get a 16" bbl.
I've got a 14.5" BCM upper + permanently welded flash hider and its great. Nice and compact. Just be careful putting it together. And for goodness sakes have a reputable smith do a solid job on the weld.
