Re: .416 Barrett
i would just shoot 50 bmg , less bullshit , if you buy a 416 or 375 , you'll need custom dies , dies that will be expensive (though , i think hornady is making some 416 amax bullets...) Load data for 416/375 is hard to find ,hard to find published g7 bc's, its even hard to find decent data for the bmg, the 416/408/375 would probably be something i would aviod , it could turn into a headahce if you cant find ammo , or if you are overpressuring your ammo , shit like that.
The AR50 is a good way to go , tested , proven , no hassle , no BS, pretty "cheap"
why dont you like the bmg ?
have you thought about the 338 lapua mag ? not a bad choice either. I see lots of guys shooting those at 1000y
you dont need a 50 bmg or 416 to shoot past 1000 yards , a 6.5mm or 300 mag , or 7mm will do the job , if you get the 140gr vld bullets to move around 2900 fps , your drop at 1000y is around 20-24 moa , which is pretty good , most 308's will drop 30-40 moa at that same distance.
my 50 cal has about the same drop at 1000y as my 6.5mm , around 20 moa , but the 6.5mm doesnt beat up your shoulder , doesn't cost anywhere near as much as the 50. The 50 has its advantages though , the splash is much easier to see compared to alittle .30 cal splash.
maybe you knew all that though ,
its really a path of least resistence questions , if you go with something "rare" or unusual , you might run into problems , problems you might have trouble fixing. If your trying to do a project , or something different with a 416 or 375 build , i would understand. But you'll be shooting faster if you go with a bmg. Look at it like this , lets say you build a custom 416/375 and you dont like it, or find yourself in need of money , you'll probably have trouble selling it and the reloading stuff. But , lots of people own BMG's , so you'd have better luck re-selling 50 bmg then 416 stuff.
but , i think lee makes 416 die , titanreloading.com i believe