The threads are 0.635" long.
https://www.brownells.com/userdocs/learn/turkishmausers.pdf

Distance from case head to shoulder is 1.948" and 1.727".
The difference is the first part of the set back 1.948 - 1.727 = 0.221"

The shoulder width on the 25-05 is 0.441" and it is 0.429" on the 257R.
The rear of the 25-06 and 257R is 0.470"
The slope of the 25-06 taper is [.47 - .441]/ [1.948 -0.2] = 0.172 inches per inch
To get from a shoulder size of .441 down to .429 it would shrink 0.012"
To shrink 0.012" on a slope of 0.172 inches per inch = .070"
This is the second part of the setback

Adding setbacks 0.221" + 0.070" = 0.291"

Thread percentage remaining = 100% - 0.291"/0.635" x 100% = 54% thread remaining.

A couple months ago I converted a Winchester M70 25-06 barrel to 257 Roberts on an Arisaka. I have plenty of barrel thread left on that project. But....

Some time ago I put Parker hale 300 Win Mag barrels on VZ24s with that much remaining thread.
The two machinists I hunt with [that hate engineers] have sneered at those projects saying they would NEVER do that.
I ask them about force, torque, pressure, steel stress...
I have hunted with them with that rifle, but they are never wrong:
https://en.wikipedia.org/wiki/Selection_bias

[Linked Image]
Parker Hale Midland rifles barrels from Numrich 10 years ago were $50, used, but bores seemed to be hand lapped... superior to ordinary factory barrels.



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The man who makes no mistakes does not usually make anything.-- Edward John Phelps