That is definitely something I will want to look into.
I am kind of reluctant about shooting it. Paraphrasing Threeband's point about if the breech were to shear it would be aimed right at your eye....
However, once I get a stock on it, I know I will be itching to fire it. Maybe use a bench rest and string.
I will want to see how it fires before and after modifying the rifling.
What about a larger caliber? Would I also have to modify the breech? Also strengthen the barrel?
Dust off my Material Science text book... Second thought. Nope.
Thanks for your suggestion...
The first thing I would do is disassemble the breech block mechanism and check the condition of the pivot pins for the rolling blocks. My thought is they are the parts which would be under the most stress during firing. Are those still available from Numrich? If so, you may want to replace them with modern steel pins and keep the originals for historical reasons.
If you install a barrel liner, it would be made of modern steel, so would help strengthen the barrel. Even so, I would start with .22 Short rounds and a string to pull the trigger for the first test before moving up to .22 Long and finally, .22 Long Rifle. I would definitely not want to try any high-velocity rounds in a rifle that old.
Larry Potterfield of Midway USA did one of his projects to do exactly what you're thinking about. Here's one of the videos about installing a barrel liner:
And, if you run this search, you'll get about 20 videos from Midway related to Remington Rolling Block rifles:
https://www.youtube.com/results?search_query=midway+usa+larry+rolling+block
Sounds like a fun project!
JoeR