Hello reiwardI'm not sure what you mean by thebecause you then say youvolume of the two rings(outside and inside)addedthem. If you mean thetotalvolume (taking the outside dimensions) and then the volume of thespace inside(taking the inside dimensions), then you'll need tosubtractthe second from the first to find the volume of iron.

Then convert, as you did, to cubic feet and hence the weight.

Grandad