They purposely designed the M91/30 bayonet to work on both (so any M91s in service wouldn’t have to have a speciality bayonet made for it after the M91/30 adoption). Early M91/30 rifles also didn’t have front sight hoods (other speciality bayonets were developed for those as well).
For historical accuracy a M91 bayonet would be most correct but ultimately there isn’t that much of a difference between the two designs, and certainly not very noticeable unless you know what to look for (say as a display piece).



























