I don't have a 10" 221 Fireball, but I do have a 12". Accuracy is acceptable.
For starters, I sure wouldn't have that gunsmith do the rechamber. Sounds like he's setting himself up to say "I told you so" when his work turns out to be inadequate. Also, I'm wondering why you wouldn't just sell the 10" 22 mag and find a 10" Fireball to replace it. The 22mag ought to bring $100-125 anyway and you can put the cost of a rechamber with that and get a Fireball. Matter of fact, if you wait til Virgin Valley has another "shorty" sale, you can just about buy a custom barrel for what you'd have in an iffy rechamber.
anyway that's my take,
Rick