I am considering building one on a late model 70 and have some questions.

Who makes Dakotas brass and how does it hold up?

Has anyone tried reforming 375 RUM brass?

What kind of velocity can I expect from the 350 and 400 grain bullets?

Thanks for any input.

I don't know the dimensions of the .416 Dakota right off hand but, I have made .404 Jeffrey from the 375 RUM brass and there's no difficulty whatsoever.

Norma makes Dakota's brass, and it's the same case as the 404.
Nominally there's about a .008" difference in the brass. Rum is fatter, so if you have a tight chamber it might be a little scary. RUM brass is cheap enough that you should just go buy a bag, measure the base and decide from there. Your reamer will tell you what the chamber clearance will be, and if it's more than .004" over the actual brass you should be fine. SAAMI tolerance is like .008" so if you have a newish reamer (.550") and smallish RUM brass (.554") you're good.
But anyway, 100 pcs of Norma's brass will last you a good long time, unless you like to hotrod.

Thanks, looks like this is do-able.

I have some Dakota brass ordered and there is some RUM brass around here already. Redding has the dies in stock and a reamer shouldn't be too big of a deal.

What appeals to me about this round over the 404 is the availability of cheaper bullets for practice as well as the slightly lower pressure than the Remmy. I have never had a problem with my 416 Remington, but lower pressure has got to be better.