Do a chamber cast ,then you will know for sure what you have .
Cast bullets are best at throat size ,if it has a throat ,some of the older rifles dont have a throat like modern firearms.
I suspect you may need to seat the bullet into the case further .
I ususlly make a dummy round from an empty case with a seated bullet ,and try and chamber it , keep adjusting the depth until it chambers .
When doing this check for rifling marks on the bullet.
I recommend CH4D dies I have quite a few sets for reloading obsolete cartridges , great people to talk to as well .

Kev.