Is the rifle (readily) adaptable to other calibres (e.g. .25 ACP)?
Just .22 rimfire, via a liner, as a really viable option.
The .25 Rimfire was larger and longer than just about anything that is still around.
Or you could dink around trying to get a powernailer blank and an adapter to work, driving a cast or swaged bullet.
There are .25 cal powernailer blanks, but they'd be tough on the chamber, and I think accuracy would be poor.
Even the adapter route is kinda hairy, as the size of the .22 is so close to the .25 that the walls of the adapter would be pretty thin.
Most of the ammo in 25 or 32 rimfire that I have seen was so corroded and covered in white crust, that a barrel is the LAST place I would want the bullet to go. Even if the corroded stuff was pretty much harmless, the cost of a couple dozen shots would cover a reline pretty nicely.
Leave the collector ammo for the collectors.
Cheers
Trev