It's missing a part.  That appears to be an all in one, reloading tool, for, as you surmised, a .25-20 rifle.  The last picture shows one half of the mold for making new bullets.  The part that is missing is the sprue cutter that is screwed into the hole on the top of the mold (left side of the first picture).  The tool could be used to make new bullets, size and deprime and reprime cartridges, then after manually filling with the correct amount of powder, seat a new bullet.

Simply googling ".25-20" indicates it was a Winchester round, from the late 1800s.  Also, manufactured using smokeless powders, once those were developed.  If I recall, I saw a video linked to from here.  Ah, yes, here it is:  https://wethearmed.com/hunting-fishing-and-trapping/25-20-winchester-92/msg363767/#msg363767.

The sprue cutter would be similar to any on a modern cast bullet mold.  Note, though, that the hole for pouring lead through must be centered over the mold cavity.  They are not all interchangeable.

What firearms are likely to have used the .25-20 rifle cartridge?

The only firearms I am familiar with that were chambered for .25-20 were the Winchester Model 92, the Remington Model 25 (the Model 25 was a neat little small frame pump also chambered for .32-20), and inexpensive bolt action rifles like the Winchester Model 43 and the Savage Model 23.

The guns are all antiques (although I did recently come across an Oregon Kimber 82 in that caliber) but .25-20 is still loaded by Winchester and (I think) Remington. Or it was recently anyway.

I rather like the .25-20, I think it should make a dandy little short range varmint round. Especially here in Illinois where it seems like there is house on every corner even out in the country. However, everyone nowadays wants at least 3000 fps out of their varmint guns, whether they really need it or not   

The only thing I have for it now is a Remington Model 25 that is really too nice to take into the field. Wish I could find another "shooter" grade gun, but so far no luck. If you want to find a gun to shoot .25-20, I'd recommend the Winchester lever gun or the small Remington pump. I'm sure Marlin made a lever gun as well. I'd avoid the Savage 23 and Winchester 43, at least for shooters. These were really rimfires chambered for low powered centerfire cartridges (like the .25-20 or .22 Hornet) and probably weren't very durable.

Oh, and neat find with the reloading tool!

Rob

There is more than one 25-20.  More than likely it is the .25 WCF.

Here is a Ideal tool in good condition:
http://www.gunauction.com/buy/5781595

Oh, no.

Cartridge controversy  .

 

The tool only reads ".25-20 R".

97% sure the markings refer to the .25 WCF aka .25-20 Winchester.  The markings are similar to other Ideal tools of that era.  It would would have been a likely companion of a lever action or single shot rifle.

There'a a museum out there that would love to have that for their Old West exhibit. Very nice!

Thanks!