Barrel set back?

[750k2]

How much of the shank can be cut and still
have enough threads for the bbl nut?
I figure I'll need 1/2" +or- for a full neck clean-up.
Trying to go from .223 to 22BR
Going from short to long is a no brainer but has anyone
went to a shorter cartridge.
Thanks for any help.

[Nor Cal Mikie]

Depends on who is going to cut the chamber. Some folks don't like to start a larger reamer into a smaller hole. Check your PMs, Mike. ;)