I have seen .25 Krags on 44 1/2, so think you would  be OK.

That might be a good idea as the Roberts can create 55,000 plus PSI with its standard loads. Cartridges based on 30-30 brass instead of the 7x57 brass are more reasonable with their smaller chamber diameters. I have a vintage .219 Donaldson Wasp barrel on an original 44 1/2 and I know that Harvey back in pre-pressure test days could load on the hot or hot plus sides but even he recognized he was pushing it and increased the case capacity by increasing the neck length to lessen the pressure slightly. I load for accuracy not velocity so it hasn't been a problem for me. I also have a 6mm 30-30 barrel for that action. A CPA 44 1/2 would have no problems.