What sort of M1a have you got? What barrel length?
If I were you I would look at shooting your M1a or AR at longer range before getting a 50cal.
A lot of competitive shooters are shooting those rifles out to 1000yards.
It's going to take you a lot of practice and shooting time to get you from 200yards to 1000+.
And for every shot you are having to fire at 200-800 you could have used a much much cheaper caliber.
If I were you I would look at getting something else that is going to be cheaper to buy, cheaper to feed and a lot lighter, less recoil and less noise.
Even if I was able to shoot at 1000yards I would pick a 338 Lapua over 50cal.
Cheaper gun, cheaper ammo and easily just as capable out to a mile and possibly further.
I don't know what accuracy you can expect from an AR50 or M99, but both the AI ASWM and TRG42 in 338 are known to shoot at around 4" groups at 1000yards, If the 50s aren't reaching that then they are no way at all worth it.
Unless you just want a 50cal and want the bragging rights of owning one and have a wallet deep enough, then by all means get one.
But practically speaking I could list at least 10 calibers off the top of my head that would suit your needs better