The only difference between 100 yards and 300 yards, is 200 yards. Really.
It's probably the shooter's fault freaking out about the distance, or shooting at too small of a target. Figure out what type of target you like at 100 yards, then blow it up for use at 300 yards. Don't try to shoot a dime at 300 yards, it's hard. Use a bigger target.
Or Possibly the bullet. You didn't say what caliber or velocity etc.
