Mike George

A small brass brush with a drop of barrel-cleaning fluid should do the trick if the threads are very dirty.

You can buy brass brushes from tool shops, but do check that the whiskers really are brass, and not brass-plated steel.

The female threads in the muzzles can be cleaned with an ordinary phosphor-bronze barrel brush, put through with a rotary motion.

To avoid carbon and muck getting into the threads, the choke tubes should be put back with a smear of grease, then the muck should just wipe off at the next cleaning.