Won't work well because you are requiring heat flux through steel (the bolt) to get to the Cu .
What you want is a thick Penny? (buy one from a coin dealer for example)? , put it on grinding paper say P80 grit? backed? by a wet? glass plate or kit bench and flatten it and then use P200 to get? smooth surface then Drill precisely in ctr using? a ctr finder if you have one ( or scribe against two chords ) or mound in a lathe chuck to find the ctr .? Cu has amazing density cw with what most people think - It's about 70% of steel. this makes it particularly good at absorbing the pulses of heat it would typically get in voice SSB operation.? (but not so good for? continuous digital modes). Brass is an unacceptable substitute .?
The big problem is the rounded back of the BS? 170? cases - potentially you can lap them to a small rectangle say 1.6mm across x the TO92 case height? by hand and a jig? for improved HT but if you have the soldered on the PCB then you are sod out of luck unless you want to do a pull and resolder job.
Obviously you? can go for? a gold plate solution where you solder small Cu fins got from material you can buy as copper shim from machinist supply houses on to the coin with? a? VERY hot/powerful Soldering iron on to the top? of the Cu coin.? The shim is used for stopping marking on workpieces held very tightly in lathe chucks and the like.?
Timothy Fidler