I am helping a friend with a rolling block project, and I may have messed it up  It is a smokeless powder military action (1901 tang patent date). I was cleaning up the metal, and when polishing the action with abrasive paper, I cut through the case hardening on the right side, directly adjacent to the chamber area, a spot about the size of a quarter. 

He wants to make this a carbine in .444 Marllin, .45/70, or maybe 44/40.  I am voting for the pistol cartridge, as the others would be a bit stout in a short carbine, but my thought is that now this action is unsafe with any chambering unless the casehardening is redone.   

I guess I am unsure of the function of the action casehardening.  Does it provide strength to keep the thing together under the pressure of the cartridge firing, or is it to prevent nicks and other exterior damage to the outside?  Thanks for any enlightenment!

Rolling block actions of this vintage were made for smokeless powder loads and were availible from Remington in all kinds of calibers including the 45-70, 30-40 Krag, 7mm spanish just to name a few. I think some have been built up in 444 Marlin, as long as the chambering you pick does not exceed a 45-70 pressure or 30-40 Krag or some of the others your OK or should be. If in doubt send it off to a good smith like John Taylor to rebuild. John did one up for me and it was great, good work and a reasonable rate.
Mike