They suggest I try and find steel ball bearins and a patch...
The Barnes still uses a sabot (diameter for a .54 cal is .50) so you lose some mass which they make up for by increasing the length. Don't Know that a solid copper Powerbelt would perform any better, but if length is an issue, they could keep the bullet slightly shorter with the larger diameter.
If you intend to use them in the Condor Protection ZoneI know a sand cast forge that may be able to make a mold for me for copper rounds or bullets