The fact that every factory rifle will not shoot all factory ammo the same is one of the most common pieces of knowledge both inside and outside the hunting community. Still, I was reminded at the range the other day that some calibers just seem to shoot more consistently than others no matter what rifle or brand of ammo you send down a barrel. For me, that caliber would be the .270 Winchester. It makes no difference if I'm shooting my Weatherby Vanguard or my Remington Model 700, they'll both put any brand of 130-grain ammo inside the same two-inch circle at 100 yards, which is about as good as I can shoot using only a forearm rest. My Savage .243 comes in a close second with any brand of 95-100 grain ammo.

Not sure if it has anything to do with it but perhaps the fact that ammo and gun makers have had 95 years to get it right with the .270 that has made the difference.

.308 Win by far.

22 LR

9mm. Haven’t found a 9mm round that my Sig P320 won’t shoot accurately enough to pass quals

No doubt 308 by miles and miles.. mine will literally group within an inch with 5 brands of ammo loaded in the magazine.

I understand development of that one dates back to the 1940's, with Winchester eventually releasing the .308 in 1952.

Yep .308 is consistent. But the the .222 is always accurate even with crap ammo

I believe the 6.5 creedmoor and the 17 HMR. Are going to pass the 308 and the 22 long rifle, if they haven't already. To inherently accurate rounds that shoot in a multitude of guns.

For what it's worth, the .308 is second only to the .223 in terms of factory ammo options currently available. At last report, there were 421 factory ammo options available for .223 rifles, with the .308 having 365 different loads being available for buyers.

Of course, these numbers are only good for those who can currently find ammo in either caliber on a store shelf.

I agree with you on the 65CM, not sure about the 17HMR passing the 22LR. I think more than 50% of the 22LR being shot is not for pinpoint accuracy, it's probably way more. Not all shooters are like us, eat up with it.

My experience as well.

.222

My vote also goes to. .308

From my own personal experience, its the .270 Win. I never have seen one of any make that wouldn't really shoot! If you are a handloader, stuff a 130 gr bullet over some 4831 & go shoot a good group. Load development done!

222 or30-06

My 6.5 CM is far more particular than my 308, not saying that it isn’t possible that the 6.5 can’t unseat the 308, it certainly has the potential to.

My 6.5 CM (Savage Model 110) is without question the pickiest rifle that I own. Shoots lights out with two different and distinct factory loads (Hornady 143-grain ELD-X and Winchester 125-grain Deer Hunter XP) but not near as much with everything else I've tried.

I clearly overlooked the fact that the .308 Winchester had such a strong following.

my .270 isn't picky about anything.

will shoot almost any 130 grain softpoint to the same point of impact at 100 yards

^^^My experience also.
.

.308, .30-06, 358 Win and 9.3x62 all seem to shoot most loads to the same basic POI

That would be my Weatherby's, since I only shoot Weatherby ammo.

+1 .308

.222 or.223

So based on the OP and title, I see why 6.5cm would be the best choice.

Most foolproof here means the caliber where u get the most combinations of factory rifle and ammo to shoot well, not necessarily the most versatile. I'm a huge 308 fan boy but it may suffer from being too successful. There's a lot more factory ammo and rifles out there. Just look a bullet weights alone. Even the fact that a huge company like Hornaday was behind developing specifically for heavier 6.5mm bullets caliber probably means all factory ammo is designed that way too. As opposed to the 308 which was military developed years ago for lighter bullets and the current civilian market for 308 is wide open.