Great handloads abound, but each rifle is different, and has it's own preferences. There are some quirks to the .204, mostly in regards to twist rate, that will make a difference. For example, a LOT of .204s will simply not shoot a 40 VM well, but MOST of them will shoot a Sierra 39 "lights out". I suggest that you look at www.204ruger.com and see what's working out for most of them. They aren't shy about posting their favorites (neither are the fine folks here, of course) Check out the "stickies" too, there is a wealth of info posted there on the .204.
I too am just working up a load for a Cooper in 204. Worked up to 26.8 gr. H335 with Rem 7 1/2 primer and 39 Sierra Blitz King yesterday. .005 off of lands for starting. Hanging into high .2's and low .3's at 100, with 200 yard groups (3) staying just under 3/4". Will play with load a bit for seating depth, but don't think I will change much. Fought a bit of a breeze and will retry when calm. Might have hit paydirt out of the gate with this load. Of course your mileage will vary, and you should work up to any load. Good luck. Russ
As somebody said, rifles are different & what works in one might not be the best in yours. I load 29.0 benchmark, Rem 7.5, Sierra 32 BK, Win brass.
That's my PD load for the cartridge.
My son shot a couple coyotes with it & it performed well on them also.
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