Sduve,.... Why not go with a 1/4" brass rod, you could have the end "threaded" to fit a 10-32 clean'n jag,.... or,... Track of The Wolf sells 5/16" synthetic ramrods and the .32 cal clean'n jags for'em (if you want flexible)!
Anyway, jest'a couple'a thots!!
I use a small diameter "treated fence post", for'a ramrod in my big-bores!!