It's more a matter of being able to see
a target at long range than hitting it. If you can't see your target, how do you expect to hit it with ANY bullet/rifle.
I'm constantly seeing posts here and at other forums about how one rifle/caliber has more range or is more accurate than another, but I don't see very much on optics. I'm in my mid fifties and still have 20/20 vision, but even 20 years ago, I couldn't see well enough to find a COM sized target and hit it (unless it was a lucky shot) at more than 150 yards without a scope of some type. Yet, I regularly read of folks hitting a torso size - or even smaller head sized - target with iron sights at 300, 500 or even a 1,000 yards, especially with military rifles. Honestly, how many people can even see
a target of that size at those ranges ~ much less hit it ~ without some sort of scope? Even with a scope, VERY
few people other than professional shooters, snipers or hunters in open country like the western/midwest US are ever required to make a shot beyond a few hundred yards, and usually at much
less. Also, the chances are that if you are talking about combat situations, the target will not only be trying to hide and/or moving, but will quite likely be shooting back!
Personally, I've found that most calibers/bullets/guns in use today will get the job done if you match the caliber/gun with your intended target... and if you plan on shooting at ranges beyond 100 yds, invest in a good scope or two. The scope will make more of a difference in your ability to hit your target (at longer ranges anyway) than anything else.