I'm not telling you what cartridge to hunt with, I am telling you that the dogma of "You need X caliber or X ft-lbs energy" is wrong. And yeah, for most people a 6.5cm is actually all they need to shoot anything in North America from 600 yds and in. You are free to hunt with whatever you'd like to, but it will help your hunting to at least be knowledgable about the subject at hand rather than repeat what you've been told your whole life without testing anything on your own.
When I hear "you need X caliber or X ft lbs" to kill deer, I'll put them on "ignore". I don't need their regurgitated data points. I got my own, from starting out as an 11 year old kid in 1976, hunting the wide open spaces of the wide open west with a Marlin 336 in .30-30. My dad's rule was that every round I shot out of that rifle had to be a handload. My handload until 2007 was topped with a 170 grain Speer Hot Core. It's "paper ballistics" look like this (DISTANCE / VELOCITY / ENERGY):
M / 2158 / 1758
100 / 1900 / 1362
200 / 1663 / 1044
300 / 1452 / 796
Disclaimer: I've been hunting mule deer and elk since 1976 and the longest shot I've ever made on a game animal was 278 yards.
However, when I was a kid, and the .30-30 was all I had, it wasn't really ever "796 foot pounds of energy at 300" that was the problem. It was the trajectory and wind drift associated with an average MV of 2158 and a bullet with a G1 BC of 0.299 that really limited my distance to 200 yards or less.
I know this because I filled 21 mule deer tags from 1985 to 2015 with a 20" barreled Ruger M77RL Ultralight in .250 Savage. My handload was tipped with the 100 grain Nosler Partition.
M / 2620 / 1524
100 / 2352 / 1299
200 / 2100 / 980
300 / 1865 / 772
In the real world, there's not enough terminal ballistic difference between the two loads above to make a difference. What difference there is that truly matters is in the exterior ballistics. Higher muzzle velocity with a higher G1 BC gives the .250 Savage load a flatter trajectory and greater wind drift resistance and make it easier to hit with. People get hung up on "1,000 foot-pounds for deer" or some other arbitrary number, but I know that a mule deer's heart pretty much explodes when center-punched with 871 foot pounds and I know from using this same .250 Savage load to tag a bull elk that prevailing weather led me to believe I wouldn't see. That shot was about 170 yards. The elk wobbled about 10 feet after taking the hit and dropped dead.
I expected that it would. In my experience, what will kill a perfectly broadside mule deer will also kill a perfectly broadside elk equally dead.
I started hunting black-tailed deer in California's A-Zone in 1984 and hunted that zone successfully every year until 2006. I filled 22 consecutive A-Zone tags shooting .223 Remington handloads out of a stainless T/C Contender Carbine (except for the first, which I shot with a stainless Mini 14).
Back in 1984, I wouldn't have considered using a .223 Remington on mule deer out to 300 yards. Even though it isn't 1984, anymore, a lot of hunters act like it is and get their nickers twisted when they ask me what I use for a "deer rifle" and "a home assembled AR-15 A4 style rifle in 5.56 NATO" is the answer I give them. If I said ".250 Savage," they wouldn't be so inclined to act as morality police. Yet, when you compare my 5.56 NATO load to my old .250 Savage load, the "paper ballistics" such folks cherish so much suddenly don't seem to matter. I'm now shooting a handload tipped with the 77 grain Sierra Tipped MatchKing -the same load I use for CMP "service rifle" and "modern military" rifle matches from the same rifle. Here it is for comparison:
M / 2850 / 1389
100 / 2632 / 1184
200 / 2424 / 1005
300 / 2226 / 847
I shot a mule deer with this load at 261 yards. It died just as dead as any mule deer I ever shot at a similar distance with my old .250 Savage load did. This load makes a higher-volume wound channel than my old .250 Savage load did and it left a bigger exit wound. I shot two whitetails with the load this past, season, too, and neither I nor the deer could tell that I didn't shoot them with the 160 grain FTX .30-30 hand load that I used from 2007 to 2024. I've killed over a dozen feral pigs with it, since deciding to try it instead of mono-metal bullets I had been using.
Shooting the same rifle and ammo in the field that I use in CMP matches has value to me that no arbitrary caliber or remaining energy dogma does. Of these three loads that I've listed, the 5.56 NATO load is the hands-down winner, because it has the highest average muzzle velocity and a vastly superior G1 BC, resulting in a significantly flatter trajectory and far less wind drift.
I'm an old geezer now. I'm pretty sure my 20th elk, which I shot through the heart at 178 yards with a 160 grain FTX handload from my .30-30, was my last. What I need in a rifle is eactly what I've got in my home-assembled AR-15 A4; a target rifle I can use in organized competition,, a target rifle that allows me more trigger time with my ammo dollars, and a rifle that is easy to hit with in the field, and has more than enough terminal ballistic authority to kill the biggest mule deer God has made a full 100 yards farther away (or more) than I will ever pull my 2 stage National Match trigger on one.
If I wanted to shoot everything in North America, I have no doubt that I could kill it stone-cold dead with a 6.5 Creedmoor, because I could have done it with my Marlin 336 that accounted for 9 of the 20 elk I've tagged. Since I no longer care to hunt elk or moose, and see myself sticking to little feral pigs, whitetail deer, mule deer, and pronghorn, I know I don't need anything more than a 5.56 NATO can deliver here in 2026.