I have used my colt Anaconda 44 magnum with a red dot scope for deer. I have mine sighted in for 50 yards. I'm using Hornady 240 grain factory ammo. I shot a small buck a few years ago at about 50 yards with no problem. I wouldthink you'd be more limited by the distance you can accurately shoot the gun at then the guns limits. My gun is accurate out to 100 yards, but it takes a steady aim on my part to be consistent at that range. The load I use has 685 foot pounds of energy at 100 yards which should be enough to take a deer. I personally wouldn’t shoot that far, but I believe you can take a deer at that range with practice.