Between you @nhenry and @Blkram you guys sure have some nice lefty rifles! That's a beauty that you'll love. Easy cartridge to load for, powders in the various 4350's to the H 4831 sc are the best all around powders from what I have seen over the years.
Nothing wrong with a fast twist 257 Roberts, you'll be able to shoot any bullet you want all the way up to the new heavyweights starting to come out now.
Same parent case so I can't see why not. With the heavier recoil you might need to make sure that the bedding is up to snuff and if it's a wood stock maybe some cross bolts to make sure it doesn't split. The Ruger Hawkeye I had in 375 Ruger did shift in the wood stock, that's how I found that...
I'm a British Columbia resident as well and yes there are large moose in the northern sections of the province especially if you are away from civilization. There are some good sized moose elsewhere in BC too but your best bet is in the remote sections of the northern half of the province.
I would like to see the long rumored Ballistic Tip Long Range (BTLR). Something like that might be less finicky than the ABLR to load. More options in the Solid Base line too.
257 130 gr BTLR
257 130 gr Accubond
257 135gr Solid Base
277 165 gr BTLR
277 170 gr Solid Base
277 170 gr Accubond
358...
I looked on their website and they are listed at 7.3 lbs and a 1 in 14 twist should be great for all but the really heavy mono bullets from Hammer and others. It will be fine for the vast majority of 35 cal bullets out there. The CVA Cascade seems to have a very good reputation too.
That's my favorite 270 cal bullet and it's on my list to work up a load in my 6.8 Western this year. Going to use Hodgdon's data for the 165 gr ABLR and work up slowly. Going to try Magpro first, what powders are you looking at?
This is their brand new design the HBC. Yes they offer heavier options in their other tipped bullets but these new ones are very sleek even compared to those.