Buzz412,
When I was headed to Africa for an all iron-sight buffalo and plains-game hunt a while back, I used my aperture-sighted .375 H&H to shoot several dozen prairie dogs at ranges out to 150 yards. After that it was relatively easy to shoot much larger animals in the right place, even beyond 200.
Elkhunternm is correct: Shooting varmints is excellent practice for big game hunting.
