Gunsmithing Barrel lengths and OD

[padronanniversary]

I am slowly piecing together a few new project. The question I have is is a 1.2" OD correct for the remington 700 action at the action side ?

They are offered in so many different widths.

Also what about a AI action ?

The other question I have for you all is what length barrel would you go for uncut for a 260 and 243 ? I assume its better to go a tad longer..more than 26" ?

Thanks in advance