Over the past several years I have contemplated what caliber I wanted and D’s decided on a 6.8. I had to sell my lower back about 6 months ago while living in Texas. Now I am back in Nc and planning my build again and thought I had it worked out again but now I am second guessing it. Somehow 300blk has jumped in my head again making me second guess the plan for the 6.8. I am planning on using it to hunt as well as range time and Maybe getting back into tactical shooting. I might suppress it at times or I might not. The upper will come from Daniel Defense and price would be the same. Ammo is around the same price. I guess I wonder at what range does the 6.8 ballistic jump ahead of the 300 blk?
My personal opinion, non scientific but the aggregate of all that I have read and seen, is that 6.8 is advantageous over 300BLK in every metric with only a couple caveats:
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Suppressed short barrel. My understanding is that this is more or less what 300 was designed for, so no surprise. 6.8 still throws quite a bit of burning gases, so if you use 6.8 for this application, expect to eat your can at a greatly accelerated pace.
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Bolt and Magazine shared by 5.56. Pretty self-explanatory.
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Subsonic ammo.
I’m sure someone with some more technical data than my opinion will chime in with some more detailed trajectory or ballistic info. Good luck.
As I currently don’t have an ar the parts swapping is not important. Cost is the same except for the 6.8 magazines. I would be running a 16" barrel and not sure if I will suppress or not. If I do decide to have a 5.56 in the future it will either be a complete rifle or complete upper.
And you can also do 6.8 subsonic ammo So that is not an issue either.
How far out do you plan to shoot?
A 9-9.5" 300 Blackout is good to 300 meters. Not sure how much is gained going to 16"?
If that fits your envelope 300 Blackout is fine, if you are beyond that, 6.8 is fine.
Out of a 16" or longer barrel, 6.8 SPC has more energy (and in most loads more velocity) at the muzzle, and retains that at all distances thanks to the generally better ballistic coefficients of the bullets that work in its case (at reasonably high velocity) vs. the bullets that are practical for supersonic 300BLK. The 6.8 SPC also has a noticeably flatter trajectory. Just an opinion that 100 yards is the distance at which the retained energy and flatter trajectory start to matter, and they would matter a lot from 250 onward. However, neither one is spectacular in either energy or trajectory.
It sounds like you currently do not have a 5.56 upper or rifle. As you may know, typical loads in 5.56 shoot much flatter than either 300BLK or 6.8 SPC and cost much less to shoot. The most ballistically efficient loads also have excellent retained energy and are much closer to 6.8 SPC energies at distance than M193 or M855. A detailed critical analysis is here:
http://www.thefirearmblog.com/blog/2015/04/04/not-so-special-a-critical-view-of-the-6-8mm-spc/
My 2 cents - for hunting larger game where you feel you need a larger/heavier bullet than a 77gr .224 SMK, I would use 300BLK out to 150-200 yards and 6.8 SPC out to maybe 250. Beyond those distances your trajectory is worsening and the velocity and energy are falling significantly. If I were compelled to hunt deer at 300 yards with an AR15 I would look seriously at a load with Sierra’s newer 77gr TMK (.420 BC) in 5.56, producing a flatter trajectory than anything with a decent BC in 6.8 or 300BLK.
For mostly hunting use a .308 Win AR with a 16" barrel is far ahead of these in terms of retained energy, offering a trajectory similar to the hot 77gr SMK loads but with double or more the energy. There are some relatively light and compact 16" .308 ARs available now. At the moment you can find quality new .308 FMJ practice ammo for 50 cents/rd, while 300BLK is generally 60-80 cents/rd and 6.8 is the same or more. If you are going to have one rifle for multiple uses, with hunting at distance a significant use, this would seem to offer more than anything in the AR15-sized platform.
6.8 over the 300 BO for hunting.
Personally used both on hunting a lot and the 6.8 just flat out puts game down faster.
This sentiment is echoed by a lot of people here in Texas for deer and hogs. I know plenty of guys that have had both and sold off the 300.
My son (11) ran a 300 BO 16" bolt last year and I am switching him to a 6.8 per his request. Building it this week.
He dropped his first two deer that went straight down with my 6.8 and him and his older brother both lost a deer with the 300.
you might want to take a look at this. a short .243 in an AR. 105gr bergers at 2900 FPS
Shot placement matters most. Either will kill medium sized game no question.
Besides flatness, my deciding factor would be that as distance increases, 6.8 loads retain an increasing amount of energy and velocity over 300blk.
From 100 to 300 yards, out of the best of these three bullets, the 6.8 retains roughly 30% more average energy of the best of the three 300 bullets.
From 100 to 300 yards, the 6.8 retains roughly 21% more average velocity than the 300blk.
http://www.shooterscalculator.com/ballistic-trajectory-chart.php?t=fe4f206e
your 6.8 and 300 blackout are 700 too 900 FTLB at 300 yrds the 6mm turbo is over 1200 ftlb
Wildcats are cool and all but he said he wants a DD upper. I’m pretty sure he wants off the shelf ammo as well.
I doubt he wants to fire form brass either.
I have both 300 BO and 6.8 SPC II. The 6.8 is far and away a better round for hunting.
In my little corner of the Country you aren’t going to find either round at the average gunshop. But, there is one within an hour of me that carries at least 1 6.8 load and a super and sub load in 300. As far as components go 30 cal bullets are far and away easier to get around here than “6.8” bullets. Now .277 Dia bullets are as easy as .308 bullets to find but most of those are the traditional 130 to 150 gr 270 win bullets. Maybe where you are the situation is different but maybe that’s something you want to look at as you make your decision
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Good shot placement trumps everything of course…
Killed plenty of deer and hogs with a 223 and cheap 55g softpoints growing up in South Texas
I was taught to only take shots that I knew were good shots and to pass if I didn’t have it.
I like the 6.8 as it leaves a little more room for error, shooting a pig on the run, etc…
Where we hunt the most it is VERY easy to lose a deer so dropping them is crucial.
I get the impression that the OP wants a DD upper, but if that isn’t set in stone, why no mention of 6.5 Grendel? The ammo is readily available online. It offers comparable performance to the 6.8 out to 300 and flat out beats it from there.
Here’s one fairly knowledgeable perspective on 6.5 G:
http://www.ar15performance.com/6_5_grendel
The author of that, who posts here as “Constructor”, is a long time proponent of 6.8 SPC but also various other calibers and offered barrels in 6.5 G for a period of time.
I’ve been watching the alternate caliber game for a long time, own two 300BLK uppers and previously owned a DD rifle in 300BLK, and came “this close” to buying a 6.8 on many occasions. I think 6.8 fills a small niche for types of hunting as discussed here. I think 300BLK was oversold, and while it is a very good choice for suppressed use or SBR’s it doesn’t offer enough benefit for other uses. 6.5 G offers some great theoretical benefits but it seems that its rim diameter makes for relatively weak bolts if using a standard barrel extension. 6.5 G in an AKM or one of the AK-47 style AR variants that has a larger bolt head would probably be a good setup.
OP, if you want Daniel Defense and are not legally precluded from hunting with a 5.56, consider their 18" barrel length options in 5.56 and a 75-77gr bullet ammo (a MK262 Mod 1 clone type load). If you don’t want that, I would go with the 6.8. Or a 16" .308 as I mentioned above.
6.5 G necked down to 6mm is bad azz.
I’m not really concerned with Paul and Harrison’s ongoing cat-fight. The fact is that the instances of people breaking bolts with factory ammo are nearly non-existent. Does it happen when you hot-rod the cartridge? It can. Does the Grendel offer credible performance from normal factory ammo? Yes. The OP mentioned range time in addition to his hunting needs. Frankly, the Grendel offers the most effective solution for both situations, and does it with factory ammo. If you are truly worried about bolt thrust, get the JP enhanced bolt or one of ARP’s.
Maybe another way to look at it is to look at overkill possibly. If an existing cartridge does it’s intended job, then what are the benefits of going with something more? What are the negatives of that? If, in the balance of that a better choice can be had then why not? Maybe 5.56 would be fine, maybe 300 Blackout, maybe 6.8 or .308 for that matter. The best choice is just that, the one that suits the users needs.
I remember hearing the phrase, “Don’t use a 50BMG for things that rimfire does as good at”. It’s an extreme for sure, but the point was made.
none of us need anything.
If you were living in Alaska and had to kill a moose to survive the winter. That is need and no one would be picking any of these calibers for that
its a toy. It is something you want. The choices are endless.
That statement is not consistent with reality. Making a blind point like that makes you a less informed and/or a less knowledgable consumer for the product for it’s own purposes.