Gunsmithing Rechambering a mosin barrel

[jeremiah_the_gunslinger]

so im working on rechambering a mosin and i know what youre thinking.... why waste the time. not for me its for a customer. im a gunsmith and ive done a few remingtons and savages in the past but never a mosin. i cantseem to find any info on how to blue print the barrel so that i wont blow headspace. anyone have any info on doing this would be greatly appreciated.