I haven't come across a Mosin that had a headspace issue yet.
If you have a concern, you can get a no go gauge
Or
measure the thickness of a cartridge rim, then put some plasti-gauge on the rim, and close the bolt. See what the plasti-gauge measures at, and add that to the rim thickness. It's cheap and dirty, but it works with rimmed cartridges.
Any auto parts store will have plasti-gauge for a couple of dollars, or if you have a well stocked garage then you already have some.
If you have a concern, you can get a no go gauge
Or
measure the thickness of a cartridge rim, then put some plasti-gauge on the rim, and close the bolt. See what the plasti-gauge measures at, and add that to the rim thickness. It's cheap and dirty, but it works with rimmed cartridges.
Any auto parts store will have plasti-gauge for a couple of dollars, or if you have a well stocked garage then you already have some.