I did some trading and now own a Proof Rifle with Big Horn Origin action. This is my first action with control round feed/non spring ejector/interchangeable bolt face. My question is about sizing my fired brass. My other actions I remove ejector and firing pin assembly then start the measuring/sizing process. When I remove firing pin assembly from Big Horn bolt the pin falls out that holds the interchangeable bolt head/face in place. What is the proper sizing method/process with this type of bolt? I was considering putting some grease on the bolt head retaining pin to help hold it in place but I'm not in love with that idea. Thanks in advance for the help!