300 wm head space gauge

[Gmac5]

I would advise against using your old brass as a gauge for your new barrel . If your new barrel has a shorter length and you set it to shoulder you will be stretching your cases ,possibly beyond there limit. Use your headspace gauges Is your new barrel factory or custom?
Gary
Will you have 2 diff rifles when finished, or are you replacing one barrel for another? If your gonna have two rifles in the same cartridge seperate your brass