Yes...but... I have done this on .308 in a standard action. As with an Improved chambering it takes some powder just to get back to equal the SAAMI performance. You lose a bit of barrel length too. The extra powder to get the hoped for advantage will cost you barrel life...as more of the powder is burned in the bore. Nit picking yes....This may explain why the "Creedmoor Clan" of cartridges is getting to be regular offerings as of late.
Not following the logic here. Why do you assume he's trying to get the "hoped for advantage" and/or will need more powder than a standard .260 Remington load?
Sounds to me like he just wants to build a .260 Remington on a long action.
