Accessories for many old American military long arms were threaded 12/24. I would use that size if I could make my own jags, scrapers, and so forth.
Shotgun brushes, loops, and jags are threaded 5/16" x 27. Taps and dies are available from Victor Tools. Some sizes of shotgun brushes can be used with our rifles, e.g. a.410 shogun brush works in a .45, and a 28 gauge nylon bristle brush will work with a .54 caliber.
Notchy Bob