Here in Montana you have to use an expanding bullet for big game hunting with any firearm so that really cuts the options down.
I have tested the Barnes X, I believe it is the 600 gr Version I ordered from Arizona Ammo Comp. They are great looking bullets but my rifle did not care for them all that much.
Plenty accurate for hunting out to 600 yards or so but I would not feel confident at any range past that with the accuracy level I was getting.
I use the 750 gr Hornady A-Max exclusively. It holds well under moa out to 1000 yards in my rifle and is technically an expanding bullet to satisfy the legal folks.
On antelope and deer size game there really is not much expansion but there is not need for it.
For larger game such as elk, the 750 gr A-Max may open up more and with a load packing 6000 to 10,000 ft/lbs of erergy depending on impact range combined with a .510" bullet of 750 gr weight, if the bullet did open up on solid bone, you may loose the back half of whatever you shoot.
The X bullet would be a better choice for heavier game simply because of its limited expansion characteristics.
I would also agree, my 50 weights 35 lbs and while that is not overly heavy for a 50 BMG, it is to heavy for this kid to pack around in the field to much.