gunut--To answer your question about which primer is best for use in the .204 Ruger, I would suggest using primers with the thickest cups you can find. The three with the thickest cups are the CCI 450, CCI BR-4, and the Rem 7½. They all have a cup thickness of .0250". The old Federal 200 has the thinnest cup of the small rifle primers that Calhoon did measurements on--cup thickness of .0190". However, the Federal 205M has a cup thickness of .0225".
If you are loading on the upper range of the listed powder charges, you would be well served to go with the thickest primer cup you can find.
gunut, my first test loads used win small rifle primers. At starting loads the firing pin crater looked deep and sacry. i now use the Rem 7 1/2 as advised on the board and have not had this issue again.
