You questions would need to be loaded with intended round/ammo of use. Need a baseline or it's unicorn farts and fairy dust. We can use a known standard a go from there. I love my M82 but it's never brough up in any "impressive" accuracy discussions. Let's say you employ a very high BC round.
Hornady 750gn AMAX - 24" barrel = ~2,820fps -
100M - Velocity: 2,716 fps, Engery: 12,284ftlbs
1,000M - Velocity: 1,883fps, Energy: 5,905ftlbs
1,500M - Velocity: 1,487fps, Energy: 3,681ftlbs
2,000M - Velocity: 1,148fps, Energy: 2,194ftlbs (barely supersonic at 1.2 miles)
Chop 250fps, 2,570fps, (I don't think you'll lose that much but for argument sake) you get the following.
100M - Velocity: 2,472 fps, Engery: 10,178ftlbs
1,000M - Velocity: 1,683fps, Energy: 4,716ftlbs
1,500M - Velocity: 1,310fps, Energy: 2,859ftlbs
2,000M - Velocity: 1,054fps, Energy: 1,850ftlbs (round is now subsonic)
The weapon is an energy king but you still need to connect. Tthe semi-auto Barretts were designed for the anti-material role and they shine in that function. Even with a match round like the 750gn AMAX you will find accuracy is sub par to other platforms. But, you don't own a semi-auto .50BMG for long range competition. You own it because it produces 12,000ftlbs of muzzle energy (in your case around 10k) and few things survive that kind of punishment. Get yourself a Magnetospeed or other modern system that will measure muzzle velocity, know the BC of the bullet in use, and employ one of the many online ballistic calculators to get a better idea of what your rifle is producing. Let us know what you find. Enjoy!