i've got the same gun and similar issues, check out my thread here:
http://204ruger.com/viewtopic.php?f=2&t=11619


I don't know if IMR4895 and H4895 are the same but if they are, it appears you are over max on the powder charge.

I've read several comments about the CCI 400's having a thin cup and are not strong enough for the 204 except for milder loads. The Hornady manual I have states they used the Rem 7 1/2 primer. I've read several comments that the CCI 450's and BR 4's and 205M's will work better due to thicker cup, but no 1st hand experience. I've got limited reloading experience as well, so.....

Check out the 204 Ruger forum, some smart people there as well and hopefully will point you in the right direction.