25-06

I do 10-20 rebarrels a year and I have only done 1 ever that had the bbl "shot out" most all of my rebarrels are due to damage, for vanity or because I guy just wants a new chambering.
The 25-06 case holds alot of powder for such a small bore rifle. If you expect to get the most from it don't settle for a bbl les then 26" Have you considered the .257 Roberts or .257 Roberts A.I.

A chambering is considered "over bore capacity" when increases in case size results in disproportiantly small increases in velocity. If you compare handloading tables for .308 Norma Mag and .300 win. Mag you would see that the slightly smaller Norma Cartridge produces MV equal to or greater then Win Mag loads useing less propellent. The Normas case size and shape works more efficiantly with the .30 bore.
I have a .280 AI. On two occasions I have allowed 7mm mag shooters I was sharing the range with to use my chrony. Both shooters were stunned to see that my .280 was as fast or faster then there factory 7mag ammo

A cartridge is not over bore because it burns more powder. It's over bore capicity when the increse in case size and charge begins to produce diminished returns. It's not an insult or a slur. It's just a clincal term to decribe a condition. Ex: a 308 win with 48gr. powder and 150 gr. slug produces 2800fps. a 30-06 with 53gr. produces 3000fps and increase of 200 fps. the 300 win mag uses 76gr and produces 3200fps. adding 5 grains increased the 06 by 200 fps over the 308. adding 22gr more in the 300 win mag added 200 fps over the 06.

the 300 win mag is over bore capicity

Mag maniac, Being able to increase speed does not define bore capacity. It's clear that we can agree do dissagree