I have a couple of NoS short chambered barrels.  
Threaded for large ring Mauser.

One is a .308Win
Other is a 30-06

Both have rather long chamber sections before the barrel begins to taper.

How much of the .308 and .30-06 chambers would have to be removed so that the .300 Savage reamer would clean up the remaining.
I have looked at chamber dimensions and tried to do the math......and failed.

Trying to determine if there will be enough of the chamber section remaining to do this safely.

Not concerned about the loss of length as the barrels are 24" and will have a finished length of 20-21".

If you were wondering, the plan is to install the barrels on 1910 Mexican Mauser actions.

Thank you for any assistance.

300 Savage is much shorter than either of the other 2 rounds.  Going to take a lot of work, I think.

Cut it all off.

Or.

Cut it off at the shoulder and use a sturdy (preferably solid carbide) boring bar to straighten out the chamber about .050 short of headspace and .050 under shoulder diameter.
Or less, if you feel confident in your measurements.

That way you don't have a crooked chamber and throat driving your reamer cock eyed.

30-06 looks like you could run the reamer in until the "case mouth's" met, then remove almost .625 from the tennon (checking headspace)
The 308Win looks like you'll need to push the start of the reamer neck just a hair passed the "case mouth" and remove about .365 of tennon.

Sound right?

Can't cut it off completely.   I don't feel comfortable that would leave enough wall thickness in the shoulder portion.
Will talk to the 'smith about the boring bar.  One of these days I'll get my own lathe.

If my rough (poor?) math was correct I had slightly different numbers , but pretty close.

I'll mark off .700" and .400" on the barrels then use a piece of .300Sav brass to get a rough idea where the chamber will end and get an idea of remaining wall thickness.