Are these typically made of copper
and then plated with something? Does anyone who's done this have any
tips (no pun intended) for me?

Smitty

We routinely sent out our tips to be silver soldered. Never any
probems. We did this in the 60s and I am sure they still do them this
way. After we got a good mechanical technician he silver soldered
them. No big deal. The silver solder was the type used in
refrigeration tubing soldering.

Bob AZ