On that 25 one would almost think it would be old, but no it is probably a .452 groove dia bbl.
You should slug your barrel - if it's .454 your O.K.
We like the cylinder exit to be at groove bbl dia or .001 above. Slug your bbl. and see.
I assume you're shooting cast bullets so as was mentioned you might try that - most moulds throw bullets several thousandths larger than the marked size on your mould.
It all hinges on your barrel groove diameter - if it's .454 or more you're AOK.
If not I'd call S&W and see what they say.