Started measuring an old spanish 94 mauser ( with the flat bottom lug ) to re-barrel and found something odd, I think ....all the info I can find tells me the thread length on this model is .645 long, but when I measure the one I have I get.585 from the face to the lug or .620 to the rim of the bolt that surrounds the case head...????????

Roger

Just measured one; .630 from receiver face to bolt lug. It's possible someone faced off your receiver ring. In any case, fit the barrel to what you have.