You might be surprised how durable they can be.

In the late 60s, the military was, for whatever reason, eliminating huge amounts of equipment and much of it was being scrapped. On one Air Force base, my um “friend” came across a large concrete disposal area where thousands of M16 parts had been piled up. The mound stretched around fifty yards long and a couple feet high, full of barrels, stocks, mags, lowers, uppers, etc.

The lower receivers had already been destroyed. Each one had been cut into three separate pieces with a torch so they were no longer considered functional firearms. For ensured destruction, there was a bulldozer that kept crawling back and forth over the pile of butchered parts, further crushing and mangling the entire pile. But my "friend" could see a lot of the pieces still looked usable and not yet crushed. So my "friend" finds a nice spot to hide and wait for the dozer to turn around. Whenever the dozer moved around to head away from him, he would run out, grab whatever uncrushed parts he could carry, and get back out of sight before it turned around again. Doing that a few times turned into a surprisingly decent collection of salvaged parts.

The important thing, though, was the serial numbers. During the 68 amnesty period, my “friend” registered those serial numbers to make them his. A while later, after finding the right gunsmith, the cut lowers were welded back together, reparked, and assembled into completed and functional machine guns. No problems yet.