Headspace is important, don't get me wrong. But I've not had a problem with any of mine. I have seven now of several variants. I bought a turned down bolt body from George Tossen on E-bay and installed it on a spare bolt. It headspaces correctly in ALL of my Mosins!
This company supplies gages to check that do not require the removal of the extractor. Work great!
http://www.okiegauges.com/
http://www.ebay.com/itm/Mosin-Nagant...-/250833575428