I would start with determining the diameter of the bore.
If a 30/06 round will not chamber i would suggest you start with a 25/06 case/no bullet. If the 25/06 case will allow the bolt to close move up to the 270 Winchester case.
If the family of 30/06 cases fail to chamber because they are too long, start with a 243 W case and go up from there meaning the 308 W will not chamber in a 243 chamber, the 243/308 W case is larger in diameter at the shoulder than the 30/06 chamber at the case body/shoulder juncture of the case. 308 W rounds have been fired in 25/06 chambers with disastrous results.
Then there is the cerosafe low temperature melt metal. Read the instructions and cautions first, most that recommend using cerosafe have never used the stuff, my opinion, cerosafe is a bad habit, it is better/safer to talk about it than us it.
I have blind end micrometers and gages, then there is always the old transfers.Then there are forming dies.
Examine the barrel for a stamp indicating the chamber, many barrels are stamped on the barrel face, for the M1917 that could be a problem with the cone face. remove the action from the stock, there are times the chamber stamp does not index on top.