The price of .22 Rf has motivated me to wean the grandsons on off of their .22's and start them on centerfire with cast. I want to go with an 8x57 1904 Steyr Mannlicher as being accurate and goof proof, easy for kids. My hope is to find a subsonic load with the 180 gr mold I have. Thinking 5 or 6 gr of Bullseye or Red Dot should get me down around 1100 fps. My question concerns tales of shortening case shoulders/headspace problems as the brass is reused. They say on here, drill out the primer flash holes to prevent that. OK. What's a good drill diameter? Do I wait for the problem to develop or should I drill them from the git go?