like any firearm, yours has its own personality and likes/dislikes, that being said, the rule of thumb is that most .204 rifles have a 1 in 12 twist and that 39 grains is typically the heaviest that will shoot well. It's interesting how a 1 grain increase will usually end up keyholing either at 100 yards or just beyond. Now some rifles have been built with 1 in 10 twist which will stabilize the heavier bullets. Check out google and you'll find a lot of info specific to this caliber.
I haven't tried 45 grain bullets yet in mine, but the 39 Sierra Blitz Kings and H4895 get along real nice (i.e. .35s for three shots at a 104 yards)and I'm still load developing!
If you're looking for coyote loads probably the two most popular bullets are the 39 SBK and the 35 Bergers.
TB