Slightly different but same case.....
My 7-08 sings with a *130g and starting JB load of Varget.
I'm not gonna get too wound up about cleaning frequency because every rig.... and every shooter,needs to figure this one out for themselves. But, "knowing"..... what the rig likes,or behavior..... coming off a deadnuts clean barrel is an easier to establish metric than letting fouling reach not only an equilibrium but also,how far it can go without cleaning. And just like "hunting" does NOT automatically mean deer whacking,although it seems that way on the intertube........ "cleaning",shouldn't be any preset level. I dry mop ALOT..... mainly because of boogers resting in the bttm of barrel. Sure,no boogers-no problems.... but it isn't an absolute. If the load is accurate enough..... I'd do just about anything as a maintenance "cleaning". Just easier for me staying closer to "bare steel".... than built up fouling. YMMV.
*130g is in the "wheelhouse" wrt weights for the chambering. So consider that when adjusting for the 308. And, I never found the "max" with the Varget/130 Lee combo. Probably could get close to another 100fps out of it? Hit a sweet node at start #'s and then went looking for game?