In general, if you had to pick just one.

Which do you feel is easiest to load for and is the most accurate out to the short distance of 300 yards?

A. 6.5 Creedmoor
B. 308 Win.
C. Too close to call?

for 400 yards and in i'd go with the 308. others will undoubtedly differ.

In my experience, the 6.5 trumps the 308, in regards to your question. Theres also less recoil, if that makes any difference

Theoretically there isn't any difference at that range other than recoil, 6.5 CM splits the difference between 243 and 308. But the 308 doesn't offer a single advantage at that range while the 6.5 has all the advantages if you ever decide to start shooting really long.

And while admittedly a small sample I've had the opportunity to shoot 5 different rifles in 6.5 CM. Every single one of them was more accurate than any 308 I've ever fired. But not by much. I'm not saying every 6.5 is more accurate than every 308. Maybe I've just been lucky buying factory loads and working up handloads

The one that shoots the 147 eld-m.

If hunting is your thing it really depends on the game and size you chase out at 300 yards. Both are good for intended use and both are accurate as hell and better than most shooters can ring out.

6.5 CM: 90 gr - 160 gr

308 Win: 110 gr - 200 gr

In my opinion the 308 Win offers a lot of punch and a lot of versatility. In the U.S. and in Africa the 308 Win is highly respected on medium and large game. I always say a short action .30 with close to 30-06 ballistics is hard to beat in the field.

I have a herd of 308 rifles, some very accurate. But if we're talking off the shelf rifles I give the nod to the Creedmoor. It has the advantage of better SAAMI chamber dimensions. The SAAMI minimum chamber for the 308 is pretty sloppy in my opinion, and factory chambers will most often be bigger than that.

Now if you put together two rifles both with "close" chambers it would be a good contest.

Here’s what the official rule book says-
Children 4 years and under use 6.5cm
Elderly 95+ Need the Creed

Everyone else will be shooting the .308 Win...

Right now I'd lean to the 6.5CM. I have shot four rifles and they all were exceptionally accurate but I must say my previous 308' s were no slouches either.
If your big game tags involve pronghorn and deer species, than 6.5 is a no brainer. But I only hunt elk and I will be looking to fill my second tag on another 6.5CM and 130gr Accubond. That load gets me 2975 fps with R16.
I did bring a Tikka 6.5 to Alaska and after ten days, found a lone bull at 1.5 miles and took the shot at 375 yards in a 20+ mph wind. The hand loaded 143 ELD-X did the job
and the bull collapsed on the spot.
Like so many correctly say here, a properly constructed bullet in the right spot is the key. Good luck.

6.5 cm.

Snap. Crackle. Pop.