You'll need to know a few more things before anyone can help you more.
1) What projectile/bullet are you using? Find its ballistic coefficient (BC)
2) What is the velocity of the projectile/bullet? A chronograph is needed. A guess can be made, but bad info in equals bad info out.
3) Use the info from above HERE. You can play with the zero range to find the match at 500 meters. Double check by using your 25 meter/400 meter results.
Keep in mind this will only get you close, you need to actually shoot the distance calculated to be sure.