Friend reminded me of one instance where you can get into trouble. many of the old single shots (rolling blocks, some Winchesters, etc.) were made in .25 RIM FIRE. Those barrels sometimes got re-used and rechambered on other rifles, and they often have smaller bores. He had a Wincester low wall in 25-20 single shot that turned out to have one of these re-chambered .25RF barrels attached (the lack of markings/proofs should have been a hint).
The other bit of confusion is that the 25-20 single shot is not the same round as the 25-20 WCF (AKA "repeater"). The 25-20 SS is an older and longer round, but some of those barrels were shortened and rechambered to 25-20WCF after the 25-20SS cases became impossible to find. Those barrels may have odd diameters.
Other than that, have at it.
Would take a look at the Speer 75gr. FN that was produced when Malin re-introduced the 25-20 (and then dropped it again). Some folks like the little Hornady 60gr., which is really more of a .256WCF bullet, but it may work for velocity seekers.
I've never owned a 25-20, but did have the loan of a Colt Lightening pump in that caliber for about a year while its owner did his tour. I was careful with this old rifle, it was in great shape, but those Colts are not known for their strenght.
Usually it got loaded with a cast bullet and a lgight charge of powder in the 1000-1100fps range. Found that 25-20 cases may just be the thinnest cases still in production, that the case that exits the chamber often has little resembelance to the case that entered the chamber (the chambers tend to let that bottle neck blow forward a good bit), and that the 25-20 is more fun that its size would indicate.
Will have to rectify the 25-20 shortage in the gun locker soon.