I also live in open country. 100 yds is not a "long shot" here. I recommend a 454. Mine are FAs with 4X Leupold scopes. I shoot 300 gr jacketed bullets and have no problem with shots 100-150 yds --- but I practice at that distance and my revolvers are sighted in @ 100 yds.

If I expect a shot much over 100 yds, I use a single shot.

It's more important where you hit 'em, than what you hit 'em with.