I'm not sure which exact gun you are looking at. Most model 25's were made in .45 ACP. However, several were also chanbered in .45 Colt. While not as common as the .45 ACP 25's they are certainly not rare. If it is an older one I would think the 4" BBL would be on the scarce side. But it may also be just a rebarreled gun.
I would like to find a nice 25 in .45 Colt. I already have a pre 25 and 625 in .45 ACP.
The gun should have a dash number. IE 25-2, 25-3 etc. If you knew this it would help with your research.