338 378 weatherby barrel length

[JamesWilson5]

Already have a 338 378 factory rifle was looking at changing barrel to a hart 30 inch for velocity. I currently have 2 30 378 weatherby one factory one with 30 inch barrel. What kinda velocity should I expect shooting from a 270 grain to a 300 grain bullets. And any opinions on hart barrel

 

[MagnumManiac]

I prefer 32"-34" finished lengths in that size cartridge.
My shortest barrel running my 300-416 Rigby Improved is 30", changed the chamber design in 2022 and very happy with it.
My 338's are running 265's and 300's at above 3300fps and 3150fps respectively, yours may be lower.
I am going to 33XC and 37XC in the near future on these instead of my wildcat, brass will be better in the long run, even though they are not volume shooters by any means.

Cheers.