The two most important things to me when buying a scope are...

Warranty, how good is it, lifetime or..., will they fix it at the minimum or replace it if it breaks or gets damaged?

Customer service, how good is it, what kind of rating do people give them?

People tell you to buy fixed as they have less moving parts and .50's can and do destroy scopes.

For a .50, its better to cry once and buy the most scope that you can afford. If anything, save your money and get a quality scope later. Some people have spent as much or more on their scopes then they did their .50.

If you have access to 1000 yards or more, you'll want a scope that can get you out there. Not just in quality glass but enough MOA also. The next thing is eye relief, you want a minimum of 3 1/2" or you might get scope eyed!

Plenty to think about before putting down your cash.