You may be onto something with this wrapping the patch around a brush for swabbing. I have made several jags on a lathe - for a specific patch thickness in a specific gun, I am looking for a "not too tight, not too loose" fit when swabbing. I use the patch wrapped around the brush in most of my CF rifles . . . should work famously in the muzzleloader when at the range.

For hunting, however, there are obvious advantages to having a combination jag/bullet seater on the rod that sits under the barrel.