6.8 SPC AR 15 Questions

I've always run my 6.8 rifles with standard buffers and buffer springs and I've never had a single malfunction. Glad to see another shooter being added to the 6.8 family. It's a great round for deer and pigs out to 300 yards or so. I

Put an adjustable has block on it and use the standard ar buffer spring.

Standard spring and buffer here. I do use adjustable gas blocks on any non-223 caliber, but not sure they are needed. ARP barrels are usually designed with the gas hole correctly proportioned for normal springs/buffers.

As much of a 6.8 SPC fan I am, I’d be remiss if I didn’t advise, the 6.5 Grendel has a firm lead in that comparison in recent times. Better component availability, equal or better factory ammo options, and way more expectation for long term sustainability. If you were on the fence about these two, step down and plant your feet on the Grendel side (or better still, the Grendel based 6mm’s like Fatrat, Turbo, 6mm AR, or 243LBC). The 6.8 is a great round, but the Grendel has a much more stable market appeal. ‘Nuff said on that, onto the meat and potatoes...

Load the SPC with Benchmark and you’ll be happy.

Standard gas lengths per barrel length will work fine, fixed port gas blocks and standard weight buffers work fine too. Running an adjustable gas block and an H2 buffer will be advantageous for ANY AR cartridge if the guy wants to maximize energy retention, minimize recoil impulse, and minimize action battering. Metered gas and extra reciprocating mass are more noticeably advantageous with high pressure, larger caliber, heavier bullet rounds in the AR, like the 6.8/6.5grendel/450/458/50.

I have two 6.8 SPC’s currently, one an 18” midlength, one a suppressed 10.5” pistol/SBR, both with H2’s, full auto weight carriers, and AGB’s. Both are extremely pleasant to shoot, and very accurate.

Love my 6.8
Standard buffer.

Ammo availability stinks. Magazine availability is worse. It’s buy online, or at academy (ammo) online only for mags. I don’t have an Academy locally yet. For a hunting AR, 6.8 is great, but for any other purpose I believe there are far better options.

Mixed Nuts said:

Is the concern that the Army will drop the 6.8 and that ammo will get scarce?

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The Army never used enough of the 6.8 to have ever made any impact on ammunition supply. For them, it's been a flash in the pan, novel idea, with incredibly limited (if any real) utilization.

10yrs ago, the 6.8 was far better supported in the market, because guys wanted something new in their AR's, and the Grendel was still under Bill Alexander's control. The 6.8 was (foolishly) overshadowed by the 300 Blackout, and now guys are realizing the weaknesses of the round, and coming back to the Grendel and 6.8. But this time around, the market preference is strongly and solidly for the 6.5 Grendel, and the interest in other 6.5mm cartridges is keeping the Grendel as the front runner, and with the "comparable product" trend in the 6.5 market, it's going to keep that position lead...

I own one 6.8 in a WC Recon; my most accurate rifle and a deer killing machine with 110 grain bullets. It is not what I would call a popular or well known round - I reload so no big deal as far as ammo support. I does a great job for me.

I love my 6.8 for deer hunting. I shoot a stiff charge of H322 behind a 100 grain Accubond. Accurate and deadly.

For deer and under I prefer the 6.8 over the 6.5 Grendel. For paper and deer I'd go with the 6.5 G

I looked at the 6.8 SPC and was going to build one. Then I discovered the 277 Wolverine. It uses the 6.8 bullet and a shortened 5.56 case like the 300 Blackout, but has a larger case capacity then the 300.
The 277 Wolverine leaves the muzzle about 50 fps slower then the 6.8 SPC. And will take deer and hog at200 to 250 yds.
The big plus with the 277 WLV is that the only thing different from a 556 AR is the barrel.

Remington threw a lot of research $ into this and found th old .30 Remington auto case ideal for the format. .277 is and was known since the 1930s at least, to be a very good , ne excellent bore size for hunting at normal hunting ranges with lighter than .30 caliber bullets for reduced recoil and higher velocity. In Remingtons experiments I believe they found that weight for weight it produced higher velolcities than the .264 calibers were capable of. They also found the 6.8 could be used in 5.56 magazine, tho optimally small mods for future purchase were recommended. That said with the bigger case than the .223 base has it really gets the 110-120 grain bullets into a useful range for expansion to at least 400 yards. I have a couple .300 BLK and lots of different 5.56, but is I was gonna go for a supersonic HUNTING round on the AR -15 format I would go 6.8 Rem from seeing and using my best friends in action on large Oregon deer to 300 yards and Monterey county hogs about the same. It has much better expansion and a lot flatter trajectory at that range than my .300 black. He uses standard 20 round mags with less than 10 rounds in them for legal hunting use and it is very reliable. I have lots of experience with .264 Win Mag and 6.5x55 and .260 Rem with those long 140 grainers, but unless you are gonna go to AR10 platform and use 6.5 Creedmore , I prefer the .270 bore for hunting and possibly more reliablity in feeding ect.

Yeah, the 6.8 SPC is very very popular for a reason - it's a very very good all-purpose round*. There's a reason why a lot of AR15 and other EBR makers offer a 6.8 but not a 6.5 grendel (Christensen, Robinson come to mind - but even much more recently than those two, some maker I can't think of eschewed 6.5 but offer a 6.8 option). The mags are known to run nearly flawlessly, like a 5.56x45 and unlike most 6.5 grendels.

*The round is named the exact opposite of what it really is - it's precisely *not* a special purpose cartridge. It IS an all-purpose round.

All this from a big fan of the 6.5 grendel.

"The 6.8 was (foolishly) overshadowed by the 300 Blackout, and now guys are realizing the weaknesses of the round, and coming back to the Grendel and 6.8"

Yup.

Plainly, anything one can imagine can be found online. But when a guy talks to manufacturers about their trends and observes the sales volumes, and then correlates local availability of products to those numbers as validating data, the trend is clear.

I’ve been building AR’s for customers for almost 20yrs, I’ve noted the shift in the last 3-5yrs in the calls I get about the 6.8 becoming more and more calls about 6.5 Grendel.

You also have to consider complimentary products in the market. The recent 6.5mm boom is a tide shift, bringing assurance of future supply of 6.5 bullets - which was already assured, to a lesser extent, by already stable and long-standing 6.5 cartridges. Equally, 7.62x39mm isn’t going anywhere, ever, so brass, bolts, and magazines will always be available for the Grendel, as the difference is 10thou more run in for the manufacturers on the bolt face. The 6.8mm shares bullets (kinda, due to limited mag length and disparate velocity) with the .270win which has already been fading in popularity in the last two generations, and its parent case is an obscure, obsolete cartridge. The fact Lapua makes brass for the Grendel and not the SPC is something in itself for some of us.

The 6.8 isn’t going to die off any time soon, but it’s certainly not leading the race these days. There are AR cartridges which won’t ever be mainstream leaders, like the WSSM’s, 7 Valk, 277wolverine, 25-45 sharps.... and then there are AR cartridges which will likely enjoy a relatively stable niche, like 7.62x39, 458 socom, 300blk, 6.5 Grendel, and 6.8 SPC. It doesn’t take much for any of these niche cartridges with proprietary cases, or obscure parents to simply slip off of the board from niche to near-wildcat, or even obsolete.

There are advantages for either, but as much as I enjoy my 6.8’s - which I just built another 10.5” 6.8 - the longevity is easier to see for the Grendel, and if you want to reach past 500yrds, the Grendel starts taking over on performance. Inside 500, the difference is moot, even on game.

If I were brutally honest, I’d skip both if I didn’t already own them and build a 6mm variant on the Grendel case. Something between the 6mm AR, AR Turbo, Fat Rat, or 243 LBC. I don’t know that I believe the claims of 2900fps with the 105-108grn pills, but I do know it runs fast enough to do what I need it to do for deer and hogs, and the slippery 105 Hybrid won’t fit in a 6-6.8 to be mag fed, so the shorter x39/Grendel case has a distinct advantage. One of these will be my next AR, and probably even be one of my next bolt guns - basically a baby Dasher with better brass availability!

6.8 spc needs special bolt, barrel, and magazines. .277 wolverine uses same mags and bolt as 5.56, just needs a new barrel.

ScrapMetalSlug said:

6.8 spc needs special bolt, barrel, and magazines. .277 wolverine uses same mags and bolt as 5.56, just needs a new barrel.

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That’s a pretty rosey picture of the Wolverine.

.277 Wolverine is also a reloader-only wildcat, which in some brass needs neck turning, whereas factory ammunition is available on the shelf for the 6.8 SPC and Grendel at any Big box store (cabela’s, dick’s, academy, scheels). The Wolverine also runs faster-than-typical powders, so it’s not exactly easy to find low SD’s, and also not exactly a new-reloader-friendly cartridge, as it will happily blow past a pressure limit with a smile on its face (whereas some other cartridges run out of case capacity before a new loader could put in too much charge, or others will give a more gradual approach to the pressure limit). The 25-45 sharps and 6x45 are much more reloader friendly in this way.

Both work, but if you’re going to extol the virtues of the Wolverine and denigrate the SPC or Grendel for needing a few readily available, but non-5.56-compatible parts, let’s paint a fair picture of what’s out there...

A regular old 20" barrel firing stiff loads of 60 gr. Partitions can accomplish anything a 6.8 SPC can.

My 6.8 SPC II upper has an adjustable gas block, mid length gas system, an M16 bolt carrier, 16.1 inch barrel, and I use an A2 rifle buffer in A2 type fixed stock because I prefer fixed stocks for hunting use with scopes. I use PRI and Barrett 6.8 SPC magazines with no problems but understand that the cheaper manufacturers reliability in function can be spotty.

Be careful about trying to outguess the market rather than getting what you want. There will always be a new kid on the block that may or may not have staying power--the newest hot cartridge seems to be the .224 Valkyrie with some holding out for the .22 Nosler, and so on. A couple of years ago, it was the .300 BO.

A lot of your choice will be what you want to do with the rifle which should drive your buying. Long range target shooting is a bit different than hunting in the brush. With the AR design, there is less of a need to try to satisfice rather than optimize by building different uppers for a particular task. That to me is the beauty of the Stoner type systems. Building switch barrel rifles in traditional bolt actions, by comparison, is a pain in the butt.

The 6.8 SPC survived Remington botching its launch due to committed folks and the 6.5 Grendel survived its proprietary beginnings due to enthusiastic adopters. Both appears decently established for now as much as any cartridge is apart from top ten rifle cartridges. Starline now makes brass for both and the 6.5 and .270 as calibers are not going anywhere soon. If Starline can make brass for long dead obscure cowboym era cartridges at a profit, then I suspect that their move into the market for rifle rounds will be driven by similar calculations. In a similar way, the rise of boutique ammunition manufacturers no longer leaves customers at the mercy of the big ammo companies. The only fly in the ointment might be continuing access to bullets specifically optimized for the Grendel or 6.8 SPC in the future but bullets do not go bad in storage so stock up on your favorites if you like them.

mshootnit said:

A regular old 20" barrel firing stiff loads of 60 Partitions can accomplish anything a 6.8 SPC can.

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Not all, in some states, caliber restrictions prevent you from using .22 caliber bullets for some types of hunting.

Hit a deer at 300yrds, the difference in 60grns and 120 becomes very clear.

Mixed Nuts said:

Adjustable gas blocks. Greyling22 mentions this, too. I'll look this hardware up. Any brands or types preferred?

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I've had good luck with BTE - cheap and reliable. But, I never change the setting. I set it to a worked up load then leave it alone. Again, it probably isn't necessary, but I just like to know I'm getting just enough gas and no more.
https://www.bte-usa.com/gas-blocks

BTE, JP, SLR, Seekins, take your pick. I use mostly JP in my personal rifles.

Mixed Nuts said:

But my specific question is about buffers, weights and springs, and the like. Does the 6.8 do better with a heavy buffer?

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I would think so.

I had a Stag Arms 20" inch 6.8 with an A2 stock and a rifle buffer. As a result I never had a problem that was the fault of the spring or buffer.

I did have to send that rifle back to Stag because there was an issue with the rifle sending rds off track and instead of feeding it into the barrel the rd would be sent into the side of the barrel and pushing the nose of the bullet into the case. They sent it back with an entirely new upper and no more problems. They fixed with without any fuss at all.

Eventually I got sick of stocking slightly oddball ammo that I either had to order online and have it shipped or buy locally for a buck a rd over what it should cost and sold it to a friend who's still whacking deer and hogs with it suppressed.

If I would've waited a few months the ammo drought would've been over and I could've found ammo for it, but whatever.

It worked a bit better than 5.56 heavy grain bullets, but not enough to justify a whole other caliber.

You might want to email Vltor and see what they recommend with that stock/buffer tube. I'm sure they've run across such combinations before.

6.8 does fine with a lightweight buffer. As long as the port size, gas length, spring strength, and reciprocating mass are all balanced together, there are multiple combinations which all function perfectly. The cyclic rate and the felt recoil impulse will vary, but they can all be made to run just fine.

Most guys prefer a slower recoil impulse for hunting with a semi-auto, and for cartridges with greater recoil than 5.56 (like the 6.8), so it’s really common for guys to run heavier carriers and heavier buffers with the 6.8. If a guy were running a 6.8 instead of a 5.56 as a 3 gun rifle, for some reason like thinking their club had stiff knockdowns, then they might want a lightweight carrier and carbine buffer...

Multiple combinations can be made to run well in the AR, and which is right for you depends upon your application.