That sounds like an interesting solution. Or you could just scrub the carbon ring out.
I am thinking buying about the same rifle, btw.
I have shot many tens of thousands of 38 rounds out of 357 revolvers. There is gunk to clean but no biggie. Also shot tons of 38 through 357 lever guns. Not an issue.
Plus you can just clean it. Worse case a little JB or Iosso.
Curious why a 357? 44 mag is just as common, costs the same for hunting ammo, and throws a way bigger load, and faster, and while they both kill, one hits much harder and is often on the edge of dropping animals in their tracks (not always but it happens)/
And bc of the expansion ratio the 44 seems to have the same or less muzzle crack (comparing my 357 and 44 mag lever guns)
I have a 44 mag single shot for straight wall (threaded). Also a threaded 1894 44 mag for the same reason. And an 1894 in 357. The 44's get taken hunting, the 357 not really.
Considering buying a 360 buck hammer to dupe 358 win ballistics in straight wall. I run mostly suppressed and the size of hole at the end of the can def matters a lot.