I personally know two folks who’ve tried them for S&G. Both are mechanically competent. Both were well over $600 into it for tooling, jigs, and multiple workpiece attempts before they realized (or more accurately, admitted) it wasn’t worth the effort and investment. If you’re one of those folks with a machine shop in your garage - like a 2 horse Bridgeport, 36” lathe, DROs, etc - then this might be a fun project. If the best you’ve got is a $500 12” floor standing drill press (or less), you’ll probably just waste a bunch of money and ruin a few otherwise perfectly good workpieces trying to build a “permanently yours” lower.
The term "80% lower" is a sales term and not recognized in the court of law. Therefore making the actual "80%lower" a chunk of material and thats all.
They are legal to purchase and complete so long as one is not barred from possessing a firearm.
These things can be costly to complete giving the fact that you will need equipment and tooling along with a short list of parts that can get expensive if you are building a quality peice. If you are a machine and tool savvy person with some good hand skills this may be a fun venture , and after a few tweaks and tuning you get a completed firearm that is yours unless you wish to register it and transfer to someone else.
I believe the 3 keys to this is: build for yourself, KNOW what you are building, don't sell it unless you go through the motions of getting the tax stamp and registering it.
I’ve got several rifles built on 80 lowers. If you’re looking into it for 1 or 2 rifles max, it’s better to just buy one built. If you’re getting into it for the hobby of doing it, theN Please do so by all means. It’s perfectly legal. Personally I fubared 4-5 lowers and at least 2 jigs before I got it right. But I enjoy the hobby of the build. And now I can do a lower in less than an hour, the tolerances are always G2G and the finish after milling is nice and smooth
I have NFA items, so my name is already on a list. I don't see the advantage of an 80% lower when I can purchase a stripped lower for around $50. I have never seen an 80% for less than that, then add in the jig, tooling, labor, etc. and it's not worth it to me.