Come on now, local marine goes nuts with armored vehicle or armed mexican military incursuion. Is that the justification your using?
I bet statisticly both are less common than so many more things to be worried about. I bet you're more likely to be snake bit while on duty statisticly than encounter any of those situations, do you wear heavy duty snake chaps? You're more likely to sustain a head injury while driving on duty or on a traffic stop than encounter either of those, do you wear a helmet while driving in your car?
Seriously,let your real and likely problems drive what you carry, don't let what you think is cool lead you to concentrate on problems that are not a practical issues.
BTW, Your 50 would have been useless against the only incident I know of with a stolen armored vehicle. What kind of vehicles does the military have in your vicinity, only a handfull of the current armored vehicles are vulnerable to 50's.
If you are taking a shot at a distance that requires a 50, in a law enforcement situation, your doing something really, really wrong.... and it's most likely your training, leadership and procedures.
As far as disabling vehicles goes, first you have to be really good to hit a vehicle with any speed, assuming you have time to deploy the weapon before it is far gone. I played around and did some tests a few years ago (having a friend who owns a junkyard has benifits!) and 30-06 AP cracked every engine block, transmission and rear end it was fired at at ranges from 100-450 yards. I imagine some in a .30 magnum caliber would be quite effective, easier to deploy and use, and much cheaper. Lets not even get into the potential liability and danger of the public taking a shot at a moving vehicle with a .50!
Sometimes I really wonder how much tax money goes into buying things with no real practical value but that are high on the "cool factor". I know I see it in the fire service myself, even in my department. Even if you buy it yourself, the taxpayers will bear the costs of the potential lawsuits, your training etc.
Think about it.