If you are loading with Trail Boss I would say Load a couple of them up, and give them a try you should do OK. I use Large Pistol standard and Magnum for Trail Boss loads in 7.62x54R loads. Again I would say load a couple and try with caution. You may end up with a pierced primer.
Do not use those primers for rifle powder loads. You will have pierced primers. It will more than likely cost you a firing pin, and maybe the firing pin spring as well. Even Magnum Small Pistol Primers can not handle the high pressure of a .204 Ruger load with rifle powder.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.