Barrett M82 A1 and a 4.5-30x56 scope with a 34mm tube. Never shot a 50BMG before nor do I do long distance shooting (at least yet), so no reference book am I. Gun belongs to a customer, relative newbie to the thing. He's looking for advice, and I'm it despite how many times that I've said that I'm not the one.

Customer has said that he's got a couple of locations that will allow him to shoot out to 900 to 1000 meters, if not longer. Because the gun's "stock" is also the receiver, I figure at least extra high mount/rings are mandatory for a proper hold. The fellow is somewhat stocky and doesn't have a long neck or tall head, but says that he shoots/gets on AR open sights well.

Barrett sells aluminum 7075 scope rings for their rifles, supposedly rated for 50BMG. Gut tells me that any mount or rings should be steel just because of recoil. But if anyone should know their gun it would be Barrett.

First name that popped up in my mind was Spuhr. But then came the uncertainty because those guys make a TON of mounts in all kinds of heights and configurations. The scope has a claimed 55MOA of adjustment available (110MOA total). A quick online calc of 750gr Hornady A-Max shows approx. equivalent of 25MOA of drop (-23'-8" +/-) at 1100 yards, just slightly farther than 1000m.

Since the scope specs claim a max adjustment of 55MOA, it would seem that a mount with no cant/tilt should suffice, right? Or should a mount with 20MOA (or more) cant still be used anyways just because of the caliber and potential range of the platform? Then there's the aluminum alloy vs steel question.

Believe me when I say that any advice would be most welcome.

check with Badger. That would be my first inquiry.

First, from my personal experience if Barrett tells you something you can rely on it 100%. If you have any concerns if their rings will work call and ask them. They will tell you straight up. Personally I don't use their rings but I would have no issue doing so.
If I was buying a removable setup I would get the Larue one and since there is no penalty for getting built in slope I would get it. There is no downside to it and some benefits.
But I personally don't have the need to take the scope off my Barrett so I don't have a removable one. I am using the Badger rings as was suggested above and they are perfect for me.

Quality rings from a good company, that are rated for a 50BMG should be good to go. Aluminum, titanium, or steel -- all should work.

The rifle may use 2 or 3 MOA obtaining a 100 yard zero. Now the scope is down to 52 or 53 MOA of up elevation. Cutting to the chase, every rifle/scope combo meant for long distance will benefit from a canted base. The further a scope is from the center of its adjustment range, the more the scope's clarity degrades. A 20 MOA (or there about) keeps the scope nearer to the center of its range for a longer shooting distance. Get a canted base for a rifle that will be shot to 1,000 yards, and beyond.

Two-piece mounts don't often have canting capabilities, but it's quite common with one-piece mounts.

Spuhr is well known. None of my rifles have Spuhr mounts. They were pretty common with tactical/precision/steel competitors, but I don't see them so often now. I've heard rumors of issues from those who shifted away from Spuhr, but I have no idea if it's just a preference thing or reality.

My best one-piece mounts are Nightforce. Lots of options for 20 MOA cants -- various heights and ring diameters. I would have no problems placing this mounts on a 50.

I would get a canted mount. You don't want to be at the limits of your scope's adjustment. Aadland mounts work very well.

https://www.swfa.com/aadland-ar-34mm-scope-mount.html

Thanks for the help. I will do the research and make recommendations to the customer based on your guidance.

Grab you some Made in China rimfire/airsoft rings off eBay. Then put a dab of nail polish on the screws, and crank those puppies down gorilla tight.

Should hold.

Rats, I found the airsoft rings, but can't find the gorilla to tighten them.

Friend of mine has been using the Geiselle big Bertha with his Vortex Razor Gen 2. He found the mount on closeout for about $275 and it has been working very well.