I've been shooting a 25-204 since 2005, it is virtually a clone of the 257 Kimber, and Gary Reeder brought it out as the 257 Raptor around 2010. Keith hit the numbers on the nose and that is from a 21" barrel, it matches the original factory ballistics of the 250-3000 and 257 Robets. It has slightly more capacity than a 25-223AI would have and with it's 30 degree shoulder feeds slick. Also case forming is a simple as running 204 brass through thru a 25-204 FL sizing die and loading. When I built mine 204 dies were hard to come by and had Hornady make me a custom FL sizing die, their 250-3000 seater works perfect.. Since then I've built a 22-204 and 6mm-204 and use a Redding Type S FL Bushing die to load the 22 / 6mm versions and have a bushing and expander to load the 25-204 with it. I will say that the Hornady elliptical expander will make brass in one pass but the Redding tapered expander will need and pass with a 6mm expander first.
Load data, I load mine to 2.41" with the 100gr due to mag constraints. Data from the 257 Kimber can be used but start low and work up.
Brass hasn't been a problem, it isn't a rifle you'd take to the prairie dog town so large quantities aren't really needed I keep 50 rounds each of 75gr(3150fps), 85gr which will be headed to AZ next month for javelina and 100gr Partitions for deer. I will say that the 75gr bullet is really heavy handed for coyotes and the only way I can save a pelt is to shoot them the long way and even then they will sometimes exit.
First deer killed with a 25-204, public land northern WI 2005, yes this was back when you could order a custom chambered barrel and a few weeks later be hunting with it.
After the work developing it and the others, there have been a lot of new cartridges introduced and I would have gone a different route. The 6.5 Grendel is only .007" larger and will fit mini actions like the CZ-527, Mini Mauser and Mini Howa and the 6.5 case has been necked to 224 (22 LBC) and 6mm(243 LBC) and you have the 22 Nosler and 6mm ARC, lots of options that weren't there in 2005. Good luck to you the 25-204 has been a pleasant journey for me.
Oh by the way you can load .257 85gr cast bullets lightly for a small game load, they are for the 25-20 and I buy them bulk 500 at a time.