it turned out to be cast pot-metal. Wouldn't take any sort of real torque on the rail mount.

And NOT all plastic is the same - but we're casual users and we don't punish our furniture the way a real soldier does.

Polymer's are like metal, they come in hundreds of grades with differing strengths and weaknesses.

But frankly, considering that the HK91 was built SPECIFICALLY as a "cheap gun" mean to be thrown away when the barrel wore out, has a sheet metal receiver like the AK and is not made with a plastic FCG housing - I can't see why it's worth thousands. It goes bang, sure, but a new barrel can run you as much as 700 bucks to have installed. That's enough for a brand new AR15!