Which round for big game AR-15?

[Todd.K]

It's 2017. We are talking about hunting with an AR. Can we leave subjectively designed "power factor" calculations to the past. They were all designed to agree with the bias of a person who never heard of bonded or all copper bullets, and never shot gel. I personally have zero interest in hunting with conventional bullets in this smaller class of calibers.

The velocity a bullet will still open at, plus have enough penetration is an objective number. One we have through testing for a lot of bullets.

The simple truth is that there is not enough difference between the 6.8 and 6.5 to matter at hunting range. I would feel good with either, and have a hard time finding a real reason to change from the one I had.

And don't buy the SPC II hype either. 5-10 percent is the chamber, the rest is handloading to "pressure signs".

[C. Stevens]

Looking in the newest Natchez catalog, I find:

6.8 SPC

-Federal Fusion MSR 115gr $20.69
-Hornady
BTHP 110gr $42.99/50
V-Max 110gr $19.69
SST 120gr $20.89
-PPU
FMJ BT 115gr $13.79
HP BT 115gr $13.99
-S&B PTS(?) 110gr $18.99

6.5 Grendel

-Hornady
ELD-X 123gr $19.69
ELD Match 123gr 19.69
...and that's it.

I haven't checked Cabelas and your local stores, but, for what you do, ammo availability would be the deciding factor.

Decide to shop at Midwayusa instead... They have a better selection of both calibers.

Sent from my XT1254 using Tapatalk

[Goldorak]

Hey, don't disparage my reading material for the most important part of the day: the crapper!

It was a snapshot of what is available out there.

[Goldorak]

"And don't buy the SPC II hype either. 5-10 percent is the chamber, the rest is handloading to "pressure signs". "

It was the chamber and the rifling twist, IIRC.
But what is wrong with "loading to pressure signs?"
To rephrase the question: why be artificially limited by over-conservative numbers? Why not push the limits past boundaries set in, let's say, questionable circumstances (the whole SAAMMI 6.8 debacle)? SSA used to have a faster "military" load, and I haven't heard of an epidemic of blown up rifles.
Maybe we should start a new topic?

[titsonritz]

http://gun-deals.com/list/ammo/6.5+Grendel
http://gun-deals.com/list/ammo/6.8+SPC

[pinzgauer]

Hmm, may be more of a Natchez issue:

https://www.midwayusa.com/product/10...tail-box-of-20

Cabela's and Academy have carried primarily the Hornady 6.8 + Grendel loadings. The federal 6.8 showed up recently, and I expect 6.5 Grendel Fusion as well.

Neither typically carry SSA, DoubleTap, AA, and similar loadings for either cartridge. They do typically have some of the Full Metal Jacket loadings by Remington for 6.8. not sure why someone would want them given the better options available through Hornady.

Debates over an additional 50 yards are useless, I agree.

The data above (and there is more) is primarily in response to the idea that somehow 6.8 has better range than Grendel does.

The objective data does not support that conclusion. Maybe hand loaders are squeezing more out of 6.8 SPC II, but then there are Grendel people doing the same with different throats. Grendel can be loaded far hotter in Bolt actions outside of AR15 mag and bolt thrust constraints. That's not of interest to me though. Likewise I'm leery of any non SAAMI loadings or chamberings that could have pressure issues. More open throats are probably okay, but nearly always come at a price

[Todd.K]

It was the chamber and the rifling twist, IIRC.
But what is wrong with "loading to pressure signs?"
To rephrase the question: why be artificially limited by over-conservative numbers? Why not push the limits past boundaries set in, let's say, questionable circumstances (the whole SAAMMI 6.8 debacle)? SSA used to have a faster "military" load, and I haven't heard of an epidemic of blown up rifles.

Twist does not affect pressure until taken to an extreme outside of any possible real world application. The belief relative to 6.8 came from an experiment with too many variables that were unaccounted for.

The reality is there was never any "SAAMI 6.8 debacle". First off Rem submitted what they were given, they didn't choose the chamber. Then ammo manufacturers tested safe loads at a reasonable chamber pressure, that were slower than the wildcat handloads made to "pressure signs". The entire thing was just an unrealistic number from handloading development that was higher pressure.

I have no interest in making or shooting loads that are close to high pressure test...

[mic2377]

I think that there really isn't too much difference between the upsized AR-15 calibers. It is splitting hairs for slight advantages either way. I would probably pick the 6.8 due to the theoretical increase in bolt strength.

I personally use a 308 Win for all of my big game hunting. It is a notable jump in lethality of anything that fits in an AR-15. Plus the the new generation of small frame AR-10's are very close to the weight of AR-15's. I just don't like chasing what I shoot...

[tom12.7]

Todd.K is right on this.

[Goldorak]

The SAAMI chamber has a wrong number somewhere, in the leade, I believe. It all came down to the way Remington handled the project. At first, they supported it, and helped the individuals R&D the cartridge. However, a lot of it was to copy and paste from the 270 Win, 'cause 270 is 6.8. Some folks realized that things are different in an AR platform, hence the many "experiments." Then, it seemed that one day Remington stopped all work, took what they had to SAAMI, then froze the cartridge and washed its corporate hands. What started out as 6.8 Remington become an orphan, and morphed into 6.8 SPC, with more development work done by private individuals, without corporate backing. The chamber is different, the pressures are higher (and not blowing up the guns), the SAAMI standard is restrictive and obsolete, yet no one can change it -because no big money company is willing to touch it. Anything else folks are doing is a "wildcat" -no matter how safe or successful. And a decade too late. So, the 6.8 SPC is an "also run", an evolutionary dead end.
Do you want to talk about "pressure breaking bolts?" Let's talk 6.5 Grendel breaking bolts made for the 7.62x39 cartridge -because manufacturers are cheap or don't know there is a different bolt face for the Grendel. Do I blame the cartridge? No!
The Grendel offers the best performance at longer distances, at 600, 800, even 1,000 yards. Better than any 6.8 or 5.56. There is a 70+ pages thread in GD on TOS, for the non-believers.
For humane hunting at ethical distances, with an AR15 platform, both sixes will do great. I stand by my suggestion that bullet selection and ammo availability should be the deciding factor.