What sort of polymer and printed with what? How many rounds can it handle before it breaks?You mean a metal-printing machine? Haven't seen any for less than tens/hundreds of thousands of dollars.3d printable lowers.
I guess you can machine the lower, but the money for the machinery and the skill to acquire them would be almost insurmountable compared to "moving" to a different state, buying a gun as a resident, and "moving" back.
Lowers can be plastic polymer...not the most accurate due to flex...but useable. We have a built New Frontier and an AR1 eXtreme (unbuilt) poly lower.
Thousands. The lower receiver isn't under any explosive pressure. The upper receiver, bolt carrier group, chamber and barrel do all the heavy lifting. Mine are commercial injection molded...but cheap printed models have survived hundreds of rounds. As more flexible printing medium becomes available, longer lasting printed lowers will be common place. At some point law will catch up to technology and a more load bearing component of poly firearms will become the serialized technical "firearm" I suspect...
As a range officer I see all kinds of ARs. I have seen several of the polymer lowers break near the buffer tube. That is the weak point because of the pounding. Some of the polymers nowadays have brass shavings in them and that helps a little bit.
I would never trust one for anything other than a .22.
I read somewhere that those failures were caused by overtightening. Not saying that is accurate...just remember reading it. My New Frontier has held up well...but I don't shoot it nearly as much as others due to it's inherent accuracy deficiencies.
The AR1 is reinforced...but that is good advice...it may become a 22lr. My wife appropriated the 1022...so I'm in need of a new semi-auto.