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Old July 15, 2012, 12:41 AM   #1
TimW77
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Comparison of the 6.8 SPC to the 7.62X39mm

Ballistics wise, how does the 6.8 SPC compare to the 7.62X39mm in an AR-15?

T.

Last edited by TimW77; July 15, 2012 at 01:07 AM. Reason: Added... "Ballistics wise"
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Old July 15, 2012, 01:01 AM   #2
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6.8 feeds reliably, 7.62x39 doesnt, the 7.62x39mm is a very tapered case, and because of this when stacked they want to arc more in the magazine, so a mag with more of a banana shape is neccessary.. 6.8 SPC is designed around the AR15 action, and isnt as tapered
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Old July 15, 2012, 05:17 PM   #3
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7.62x39 doesn't feed well because the cartridge wasn't designed to feed in an AR type magazine. Rock River has addressed this problem by making an AR that uses AK magazines. This problem has always been the Achilles heel of trying to match the 7.62x39 round up with an AR platform.

I have owned ARs that shot both types of rounds and got rid of both of them. I'm on a waiting list to get the new Rock River LAR-47 that I mentioned above. From my reading and research I've concluded that the 6.8 SPC is ballistically superior to the 7.62 round as far as long range accuracy goes. The AK round will never be a tack driver but up close it can't be beat.
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Old July 15, 2012, 06:15 PM   #4
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What about 6.8 SPC versus 300 Blackout?


(duck and cover)
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Old July 15, 2012, 06:33 PM   #5
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...and the Grendel
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Old July 15, 2012, 07:22 PM   #6
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From what I've read they're all good cartridges but not in wide use. So unless the military starts widely using them they'll never get out of the starting block. So far at least only three bullet makers that I'm aware of produces the 6.8 SPC; Remington, Hornady & Silver State Amory.

I don't know anything about the Grendel or the 300 AAC.
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Old July 15, 2012, 08:00 PM   #7
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the Grendel is ballistically similar to the 6.8 out to about 400 yards, then its superior bc allows it to surpass the 6.8 past those ranges. (at about 1000 yards, the 6.5 even surpasses the .308). The 300 AAC blackout is an alright round as well, however, being a .30 caliber round, it's trajectory is not as flat, many people claim that it's maxed out at about 300 yards, it was originally built for suppressed weapons, and the power is close, but not quite equal to the 6.8

I love the idea of the 6.5, however, due to my budget restraints I went with the 6.8 SPC for my ar system, as the 300 aac didn't seem to be advantageous over the 6.8 in hunting of deer.
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Old July 15, 2012, 08:05 PM   #8
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Do u hunt deer with it and if u do what's the terminal performance like?
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Old July 15, 2012, 08:29 PM   #9
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i did some ballistics research on the 6.8 SPC and 6.5 grendel, ballistics werent equal until about 800 yards out.. perhaps the grendel fans were testing their loads with the standard length 6.8mm bullet, however, i also tested the maximum bullet lengths for an AR15 type magazine in both tests i ran as well, SPC had a slight edge out to about 800 and the grendel only gained a slight advantage after that... see, what the grendel gains in a better ballistics coefficiency to conserve energy, the 6.8 has more to begin with, and only a slighter lower BC..

so if you compare that with the face the 6.8 feeds better in the magazines, has more of a capacity, and has a huge aftermarket backing (6 individual 6.5mm loads available on midwayusa.com and 30 available for 6.8) the 6.8 has the clear advantage

i too was also curious about the .300 AAC blackout, but wasnt too impressed with it ballistically, downrange its going to drop pretty fast, though it can take pretty long .308 caliber bullets, the overall velocity of the rounds negate the BC of the longer .308 bullets, with the heavier .308 bullets i see this being well suited with a suppressor and sub-sonic ammunition, for anything else i think it comes up lacking in all areas compared to the other options


my vote easily goes for the 6.8mm SPC for reasons listed above

Last edited by jason41987; July 15, 2012 at 08:44 PM.
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Old July 15, 2012, 09:11 PM   #10
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au contraire mon ami, the Grendel picks up the advantage almost immediately since it's 6.8SPC competitor
has the disadvantage of powder-limited capacity in the parent case. That means for the same useable
powder space under the 6.8's optimized 113gr bullet, I can put a 123gr 6.5 projectile in the Grendel.

(Try it in QuickLoad some time. The .277/115grSMK in the 6.8Rem and the .264/123grSMK in the
Grendel have exactly the same usable powder volume when seated to 2.25" for the AR magazine.)

The result is pretty much this:

http://www.alexanderarms.com/images/...er-article.pdf

Truth-in-Lending:
Granted, this is a Shooting Times article on the Alexander website, but my own Grendel performs exactly as advertised.

Last edited by mehavey; July 15, 2012 at 09:20 PM.
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Old July 15, 2012, 09:46 PM   #11
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sure it does, if you want to use a moderate 6.8mm load with the shortest bullet available, ive seen loads with close to 2800fps from the muzzle in 6.8 and if i was going to make a long range load i would use the 130 grain hornady interlock sst bullet, ive ran the numbers with different loads and found at 1000 yards, 6.8mm SPC and 6.5mm grendel were actually only about 50ft/lbs of energy different at 1000 yards and equal at 800, in a cartridge that actually chambers well, and has aftermarket support the 6.5mm grendel will never receive due to it requiring a single stack magazine and having feeding issues

if you want to go beyond 1000 yards target shooting, go for it, its not going to be useful for much beyond 800 anyway due to its velocity being way too low for expansion, unless all you were planning to do is scuff a metal plate.. face it, in a war between the 6.8mm SPC and the 6.5mm grendel, the grendel lost, the aftermarket has decided and thats why ill go 6.8mm SPC
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Old July 15, 2012, 10:46 PM   #12
mehavey
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Quote:
if you want to use a moderate 6.8mm load with the shortest bullet available
The 113gr projectile provides the 6.8 it's max ballistic performance when having to balance
residual powder capacity against seating depth req'd of a AR platform (the OP's original question).
Quote:
...would use the 130 grain hornady interlock sst bullet, ive ran the numbers...
Quote:
6.5mm grendel will never receive due to it requiring a single stack magazine and having feeding issues...
Never had a failure to feed or extract in more than a thousand rounds.

Use of a 130gr bullet requires it being seated well beyond the 2.26" max length of the AR magazine
or you run into the same case capacity problem mentioned earlier. (In fact Hornaday 8th lists
their 130gr interlock/6.8Rem OAL as 2.355")

What does "single stack magazine" refer to? The Grendel uses a standard AR double-stack magazine design.
(In fact I once used my AR-15/5.56 magazines on a dare ...which functioned fine.)

Last edited by mehavey; July 15, 2012 at 10:53 PM.
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Old July 15, 2012, 10:56 PM   #13
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For those that answer without reading...

Let's try this again!

Question was, "Ballistics wise, how does the 6.8 SPC compare to the 7.62X39mm in an AR-15?"

Simple enough?

No 6.5 Grendel, no .300 Blackout, no .308W.

No comparison of the 6.5 Grendel to the 6.8, no comparison of the Grendel to the .308W.

T.
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Old July 15, 2012, 11:08 PM   #14
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The 6.8 spc is roughly 300 fps faster 200 more ft/lbs energy slightly more recoil energy. But similar recoil speed. Compared to 7.62x39. Hope that helps
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Old July 15, 2012, 11:32 PM   #15
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i would say in an AR platform, 6.8 delivers more power, more range, better ballistics, and is reliable in the forum, the 7.62x39mm ammo is cheaper to fire and provides sufficient performance out to 300 or so yards, but doesnt feed well due to the caper of the case.. HOWEVER, something like an AR47 lower receiver allows AK47 magazines to be used for more reliable feeding in the rifle, and i recon with a little skill someone could convert an AR15 lower to an AR47 lower and use AK banana mags for reliable feeding if you really wanted an x39 in an AR15

in a standard AR15 though, the 6.8 will function so much better hands down
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Old July 15, 2012, 11:48 PM   #16
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I have a 6.8 and am very happy with it's performance.
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Old July 16, 2012, 12:45 AM   #17
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Quote:
The 6.8 spc is roughly 300 fps faster 200 more ft/lbs energy slightly more recoil energy. But similar recoil speed. Compared to 7.62x39. Hope that helps
Could not have said it better myself. Some people attempt to say that the 7.62x39 is close to the 6.8 (mistakenly). That 100-200 ft/lbs of energy is nothing to scoff at.

Also: my apologies for the comparison to the other two cartridges, I got carried away.
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Old July 16, 2012, 05:53 AM   #18
mehavey
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Quote:
Question was, "Ballistics wise, how does the 6.8 SPC compare to the 7.62X39mm in an AR-15?"
See the last two columns in the post #10 chart above:
http://thefiringline.com/forums/show...6&postcount=10


reference for most common ammo:
http://en.wikipedia.org/wiki/7.62%C3%9739mm
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Old July 16, 2012, 08:47 AM   #19
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something else it doesnt seem people realize, is surplus sources of cheap 7.62x39 is drying up, most countries that used that cartridge before havent used it in decades so it is running out, which means we'll be stuck with factory sources for this ammunition and the general cost to fire this round will be closer to the other common rifle cartridges in america... so the savings at some point are going to go away with 7.62x39mm
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Old July 16, 2012, 03:24 PM   #20
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I have 6.8 and 300 blackout, but I like my 300 blackout better because I can go subsonic and supersonic, use my 5.56 brass and the magazines are plentiful. Not so with 6.8
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Old July 16, 2012, 04:19 PM   #21
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Ive got an 6.8 SPC II that I built and have taken a fair amount of game with it.
The two best hunting bullets I have used are the 95gr Barnes TTSX and the 110 Nosler Accubond. I load both in Hornady brass over H322, seated to max magazine length, lit by a BR4 primer. They both give complete penetration and good expansion on whitetails and feral hogs. I shot a 100lb doe quartering to me and the TTSX smashed her shoulder and penetated lengthwise before embedding itself in her pelvic bone. Ive shot several 150-175 lb feral hogs through the front shoulders anchoring them on the spot. That told me everything I need to know about the cartridges real world performance.

Ive never shot a 7.62 x 39 weapon that impressed me enough to buy one.

FWIW I can find 6.8 SPC ammo in my local gun shops if needed. Ive never actually seen a box of 6.5 Grendel ammo for sale... anywhere.
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Old July 16, 2012, 05:29 PM   #22
mehavey
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Quote:
Ive never actually seen a box of 6.5 Grendel ammo for sale... anywhere.....
Both of my local GS's here in NoVa have it -- Clark Bros & Virginia Arms.
On the downstroke, I've never seen 6.8....
(then again, maybe I haven't looked)

FWIW: When wolf starts producing a cartridge...
http://www.aimsurplus.com/product.as...ox&groupid=247
You have arrived.



I now return control of the thread to the original topic.
and beg forgiveness of the Moderators & OP.

Last edited by mehavey; July 16, 2012 at 05:41 PM.
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Old July 16, 2012, 06:12 PM   #23
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You'll never get the grendel and 6.8 people to live together. Such is life.

Anyway, I've been shooting my 6.8 SPCII in 600-yard F-class matches for a few months (I'm no good at it, but the round isn't the problem ). When you say "ballistically", right now I think of the curve. Run a few numbers, and you'll see that the 6.8 defeats the 7.62 fairly handily in the drop and energy department once you get far enough out. That 7.62x39 doesn't exactly have the best BCs.

Not like you're going to take a deer at 600 yards with 450 ft-lbs, but hey. It is a ballistic differentiator .

I'm not running anything particularly hot, but my load gives me a max PBR (according to JBM) of 309 yards. For something that gives me more warm fuzzies (terminal-ballistically) than the 223, I feel pretty good about that.
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Old July 16, 2012, 06:18 PM   #24
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Quote:
So far at least only three bullet makers that I'm aware of produces the 6.8 SPC; Remington, Hornady & Silver State Amory.
BTW, there are more than three now:
  • Hornady
  • Remington
  • Cor-Bon
  • SSA
  • Sellier & Bellot
  • Doubletap
Plus, there's a vicious rumor that Tula will be releasing an inexpensive FMJ in 6.8 SPCII sometime 'round the end of the year. Of course, the S&B is fairly inexpensive (comparatively speaking) these days already.
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Old July 19, 2012, 12:44 PM   #25
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Mehavey, I saw the ballistics chart that you presented in a popular magazine. I thought the 6.8 stats in the chart seemed anemic from what I know about it. I found another chart that showed the 6.8 with the TSX 110 gr. While the muzzle velocity is nearly identical, the rest of the specs aren't. Bottom line is that the 6.8 110TSX is traveling @ 1439fps @ 600yds, not the authors stated 1287fps.

What we all want is a do everything weapon, and a lot of us hoped the SPC was close. The 6.5 Grendel is the perfect storm. It just happened to have the right BC for the velocity (~2700fps muzzle) and the typical "off the shelf" twists available. The 6.8 SPC suffers from the same issues the 7mm-08 did. In order to have the perfect BC per velocity/SD/Mass and all that sort of thing, you had to load a projectile that was too heavy to be safely propelled to that magic 2700 fps mark. And even if you could, you defeated your purpose anyway... that being... superior ballistics with minimal recoil.

I do believe that there is a perfect storm combination for the 6.8 also. But I think that it involves figuring out how to launch a ~130gr HPBT @ 2700fps with an appropriate twist to stabilize the bullet.

Just my .02
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