9.3,
I don't know how the M-617 would do since the bore would be the .224 and you are going from a rim fire to a center fire. I suppose one could bore and rifle the barrel to .257, but the frame issue to center fire may pose a problem.
Lap the bore, re-crown the barrel, and check the throats on the 617 if you haven't already done so before you give up on it.
As previously mentioned, I started with the K-38 Spl. and sleeved the barrel to .257" and had an M-17 22RF cylinder fitted and bored to 25-20. You would already have the cylinder, so it may be a wash unless its a 10 shot. My cylinder is a tad short since it was for the shorter .38 Spl. and 22 RF, but works OK. Had I thought about it at the time, I would have done what Drilling Man did and started with the M-19 and used an M-48 cylinder.
I do know you won't have any problems with the brass and loading if all is done properly and will be well pleased with the results. Any stretching, splitting or other problems can most likely be traced back to bad chambers or headspacing, improper reloading techniques, or in the case of Remington, bad brass.
Or, you could go with a .257 Magnum and start from scratch, which is what I was going to do, but decided on the 25-20 instead and haven't looked back.
David