Know your strengths and practice your weaknesses until they are no longer weak.
This goes for spotting, stalking, range estimation and marksmanship. As far as guns go, a .30-30 can be just as effective as a .270, provided you taylor your hunt to play to it's strengths. Don't get too hung up on caliber, just learn to shoot it well out to 300 or even 400 yards, and learn what 300 yards of prairie looks like. Also, learn to get on target at 100 yards quickly, before he starts to run again.
Actually, here in MT we shoot a lot of speed goats on the run, but usually at less than 100yards. That is because the herds get bounced around a lot on opening day, and you are as likely to blunder into them with a pickup on a field road as you are to stalk up on one. It is a simple math problem. Once you know the proper lead, use the known approximate length of a goat, say 4ft, to measure your lead. While swinging your lead, deliberately press the trigger when the horizontal wire is on the animal.
Seriously though, DO NOT LEARN ON GAME ANIMALS: get a few old tires and some plywood. Make rolling targets with 10" centers and find a steep hill. Get them rolling about 15-20mph and shoot them with a .22 and SUB sonic ammo. The target is only 1/3 as fast as an antelope, but your ammo is 1/3 the speed of most big game rifles. The lead will be the same. Practice, practice, practice, out to NO MORE than about 100 yards. This shot CAN be mastered.
You'll probably never NEED a gun. I hope you never do. But IF you do, you will need it worse than anything you've ever needed in your life.
IF we're not supposed to eat animals,
howcome God made 'em outta meat?