I shoot the 25-20 in several types of actions and use a little different technique for my SS's. If you can find a Lyman M die it is a little easier.
Basically when I bell the case mouth I want enough that I can get the bullet base well into the case mouth that the case can hold it without tilting in any direction.
Guide the round into seating die, seat and crimp separate operation if I am using a crimp.
Those case moths arethin and need special attention since they aren't going to take any mishandling as you know.

Hope that helps.

Bob

If it's not too late, look into these expanders that NOE makes, for use in the $20 Lee "Universal Expander" (which it's not) die body.

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Glenn 

CH 4D short die body has the same internal thread as the male neck size die and M Die plug. Put the body in your  press. Neck size, remove the sizing ring & top ring lock plug, screw the M plug in. It’s the M that sets final neck diameter and flare.

Minimum working the brass rarely lose a case. All you need to finish is the seating die. If you want my sizer & M plugs diameters & bullet sizes for 25/20 WCF can post, they are probably close to correct for your rifle. M diamaters can be trial and error. Another caution M die bodies come in various lengths generally short cases need short body. 38/55 based need Medium.  

To be clear how it works, neck sizer over sizes just a bit, not nearly as much as a factory full length. M plug opens the neck up to correct for YOUR bullet then flares the cases mouth with very little brass working.

Rule of thumb cast bullet with a small bullet wants about .002 neck pull. Jacketed bit more. This general, some prefer more or less. Cartridges working  through Lever actions and spring magazines need more pull than Single shots. Less than case full of smokeless powder needs more pull than case full of black when the bullet sits on powder and a wad. More pull can give better combustion.

My opinion best solution any cast bullet fixed loading. I use the method 25/20 WCF 38/40 WCF 30/30 32/40 & 38/55  two die bodies 5 sizing rings 5 M plugs to load 5 cartridges.

Make sense ?

Boats

Be careful in setting up the M die. I unscrew. The expander plug and adjust the die body. Place case in and run into die body. Reinstall expander and run it down until you make contact. Let case down and screw expander in and continue until you get the correct bell. Run case in and lock down the expander. when you get the bell you want. Go easy on the adjustments.
Use that case as your max length or you get too much of a good thing on a case longer than one used to set the bell.
You're good to go.
Good luck and hopefully your loss rate goes to zero.
The 25-20 is a great cartridge.

Bob

Have to answer in couple of messages due picture size.

Most call expanders “m” dies, think M is Lyman’s name for expander dies, CH 4D calls them expander dies. They are quite different.

CH dies are on the left. Expander is a ball, after it expands its clear of the case neck until the neck flare section comes into play. Expanders on the right are Lyman’s. Long expand surface and sharp flare step.

New cases Sequence is neck size to uniform mouth, trim, then de-bur, this is a CH tool run on a power screwdriver.  Last step is flare 

Boats

Here are the die body’s internal parts.  Bushing plug has its primer knock out mounted, use it sometimes mostly de prime separately.  Note two bushings one is a spacer on top of the correct bushing due 25/20 case length.

Expander plug shown too.