I'm hoping to build my first AR10 next year and am trying to settle on a caliber. I always thought it would be a .308 but now I want to at least look at other calibers such as the 6.5CM, .260Rem, etc.

I'll be using it primarily for hunting, with maybe a little bench rest shooting mixed in. I don't have access to a range that has long range shooting available so my longest likely hunting shot will likely be under 400yds.

For the above applications, would there be any real benefit to going away from the .308? Or stick with .308 and the abundantly available ammo?

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For the above applications, would there be any real benefit to going away from the .308? Or stick with .308 and the abundantly available ammo?

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1) No
2) Yes

Agree with Gibberish. 6.5 is better at long distances, say past 500 yrds. 500 and less, go with 308 for better ammo availability and longer barrel life.

I don't have ready access to ballistics info at work, but a 140 gr 6.5 bullet will likely deal with wind better than the bullet weights a .308 typically uses.

I have had both and prefer the 6.5 CM, but I stretch out farther than 400 yards. For your requirements the .308 is probably a good bet. Ammo is easy to find and still plenty accurate at longer ranges. It was also have a ton of options if you ever want to load your own.

If you don't reload...I'd stick with the 308Win.

I do reload, but one thing about the 308 thst intrigues me is the ability to find ammo in a pinch or scrounge up if SHTF.

Why not do both? From what I understand you can swap between the two with only a barrel change. At least that's what I gleaned when I researched for my 6.5CM bolt rifle I just put together. You obviously may need a few more parts going with an AR platform, but who says you can't have both?

That's an option down the road for sure, but gotta start with just one

If I were going to want both, I wouldnt just swap the barrels. Much easier said that done especially for practical purposes. That would definitely be a have two separate uppers situation.

True. After I made the comment, it kinda hit me that it would be easier to just have another upper chambered in 6.5.

I don't think you can really go wrong either way, but I do have to order my ammo online which can limit how much I shoot and how often if I don't buy enough at one time. It's not as easy as walking into the local gun store to pick up a couple hundred rounds.

+1 for the 308. at those distances you're really not gaining anything of consequence. i would go with the 308 simply because i can shoot 50 cent range ammo (brass not steel) out of a nitrided barrel.

to compare apples to apples @ 400 yards i ran hornady superperformance sst ballistics
308 - 2075 fps, 1577 ft-lb, drop 29.2", drift 12.7" @ 10mph, ~$1.50 per shot
6.5 - 2223 fps, 1415 ft-lb, drop 25.9", drift 11.0" @ 10mph, ~$1.65 per shot