This -><- close to choosing 6.8 SPC vs 6.5 grendel

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Originally Posted by constructor

Yes there was. The SAAMI print had a .050" long freebore. The 115gr bullets Hornady made at the time were jammed into the lands… Chris Murray has said before the print turned in to SAAMI was an early design…

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Yes, the more “match” chamber design got sent to Remington, who sent it to SAAMI. SAAMI simply published the new standard as it was submitted, they didn’t mess anything up, or guarantee it would match development hand load velocity. Some early bullets were not well designed for the submitted chamber, they needed to be redesigned. These were both minor issues and not some giant problem that should have doomed the 6.8, but for the proponents overreaction. I never saw 50-100fps being worth turning off a huge chunk of people who won’t own one now. I still think it’s the most practical amount of power you can fit in an AR15.

Bringing in an industry partner for more of the development, not just to submit to SAAMI, and more development with ammo manufacturers are lessons mostly learned.

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Originally Posted by constructor

A mistake on a reamer print from PTG around 2006 caused the second problem.

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That’s a manufacturing problem, not the SAAMI spec. I’m actually the guy who noticed the shaved copper rings.

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Originally Posted by Todd.K

Yes, the more “match” chamber design got sent to Remington, who sent it to SAAMI. SAAMI simply published the new standard as it was submitted, they didn’t mess anything up, or guarantee it would match development hand load velocity. Some early bullets were not well designed for the submitted chamber, they needed to be redesigned. These were both minor issues and not some giant problem that should have doomed the 6.8, but for the proponents overreaction. I never saw 50-100fps being worth turning off a huge chunk of people who won’t own one now. I still think it’s the most practical amount of power you can fit in an AR15.

Bringing in an industry partner for more of the development, not just to submit to SAAMI, and more development with ammo manufacturers are lessons mostly learned.



That’s a manufacturing problem, not the SAAMI spec. I’m actually the guy who noticed the shaved copper rings.

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I know it wasn't SAAMI spec. someone at PTG transposed a number, it should have been 1.7109" not 1.7019".
"A guy that noticed the copper rings". In Jan 2006 I unloaded a cartridge and stuck on the bullet was a ring. I called Art and asked him about it, he just said it happens but wasn't sure why at the time. Later that year I found the transposed number on the PTG print and tried with 6 emails to get Dave to understand the mistake. I finally gave up and designed a new reamer with a 35 degree angle at the end of the case mouth and .085" freebore and told PTG to just make the reamer as I had drawn it. I went back and forth with them for a few years because sometimes they would just send me a standard 6.8x43 reamer instead of using my drawing. I ended up going to JGS for all of my reamers.
At any rate the reamer everyone calls the SPCII is the one that has a .100" freebore and we have proven several times over we can load heavier charges and get a lot more velocity in barrels using that chamber.
At a time when every other statement was "the Grendel shoots flatter" the extra velocity was important for comparison to show the level of performance the 6.8 could have when made correctly. Guys that want to go to the store and buy ammo off the shelf can still do that. Guys that want to shoot 130 gr Bergers at 2600fps can do that too.

I used to work at Noveske. So when I found the rings Johnny, Art, and Dave got the problem figured out.

I agree the longer freebore is more appropriate/better for an AR. But It’s not reasonable to believe your velocity numbers could be attained in a pressure test barrel. The majority of the velocity loss was proper testing for commercial loading and not the match chamber.

All this focus on a little velocity is still turning off a lot of potential users from a really useful cartridge.

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Originally Posted by Todd.K

I used to work at Noveske. So when I found the rings Johnny, Art, and Dave got the problem figured out.

I agree the longer freebore is more appropriate/better for an AR. But It’s not reasonable to believe your velocity numbers could be attained in a pressure test barrel. The majority of the velocity loss was proper testing for commercial loading and not the match chamber.

All this focus on a little velocity is still turning off a lot of potential users from a really useful cartridge.

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So you guys were using the SPCII reamer design from PTG and that is what John called the mod 1?
We ran the tests with a Pressure Trace system and I made a piezo test barrel for Art in early 2008. I think all of the SAAMI and SPCII wars were fought back in 2007 and 8 and everyone understands the value of the SPCII or other improved chambers and rifling.
I was getting blanks from PAC NOR back then until fall of 2008 and tested 11, 12 and 13 twist barrels, they made the 12 twist button for me after we completed the 6.8 performance test down at Wild River Ranch in Texas. Seems like you guys changed twist rates shortly after, you guys used to make your barrels at PAC NORs facility didn't you?
We tested several barrels but the difference between a 13 twist 3 groove with my DMR chamber and a DPMS with 10 twist SAAMI chamber was 13,000psi (DPMS 13k higher)using the same SSA ammo, from the same box.
As for tuning some people off, yeah I guess it could have but I still can't make 6.8 barrels fast enough to meet the demand and that isn't why the military didn't adopt it. Even Mattis said they couldn't justify the expense, loved the idea but couldn't approve it.

The move to 12 twist came with John’s take on the SPCII chamber. I never got too deep into all the chamber details but I know it had similar freebore.

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Originally Posted by Steve_in_Allentown

You're right about the original SPC chambers not allowing for the use of high performance ammo. To the best of my knowledge it's been many years since anyone has produced barrels using the old SPC chamber specs.

Remington did a very poor job designing the chamber because they were in a rush to get what they saw as a gold mine into the hands of the military. They were so driven by their desire to pump up their bottom line that upper management forced short cuts to be taken which neutered the potential of the cartridge. The chamber designs were unfinished and the barrel rifling was the same as the 6.8's parent round the .270 Win. All of this resulted in lackluster ballistic performance which is why the military didn't adopt the cartridge.

Remington abandoned their development efforts and these days the only ammo manufactured using the anemic ballistics of the original SAAMI approved 6.8 specs is that produced by Remington.

All of the design mistakes made by Remington have been corrected. The result is the SPC II which is a huge leap forward from the original design. In fact, I'm unaware of any manufacturers building anything using the old SPC designed chamber today.

Reloading manuals still show loads based on the SPC SAAMI specs. Folks that are into the 6.8 use the max loads in the those reloading manuals as their starting loads and work up from there. I imagine that at some point SAMMI will approve standardized SPC II specs. Obviously, you can't be a moron when working up handloads so be sure to read the manual to see if it specifies the loads as being SPC or SPC II.

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I’m genuinely not trying to stir up things here, but this needs to be addressed.

We have a lot of new reloaders. Experienced reloaders already know not to do the above, but some younger or new reloaders might read this and think that it’s sound advice.

It simply isn’t. You don’t take max load values and use them as starting loads, no matter what kind of chamber you have.

There have been industry engineers who actually get paid to run pressure test equipment that is calibrated and vetted who compared both the SAAMI chamber pressure data with their pressure test breech, then used a SPC II reamer in the exact same instrumented barrel. They saw an average of 19fps difference from a 24” barrel, loaded to the same pressures.

I would recommend editing that post.

I don’t have much time anymore to log in and post, but I came across this and felt that it needs to be addressed from a safety standpoint.


Looking over the thread, there are several other technical errors and biases with incorrect velocities represented.

For example, you don’t normally use G7 drag models for trajectories within 600yds. G7 models were specifically meant to represent a Spitzer bullet with boat tail after 600yds for long range shooting to get more accurate predictions since G1 models are progressively optimistic once you pass 600yds.

Within 600yds, the G1 model works very well.

With the AR-15, it really behaves well when you keep pressures tame, rather than trying to turn it into a magnum class pressure vessel.

For ammo availability, I have a plethora of LGS and large National chains within 30-45 minutes of me, with another Sportsman’s being built within that radius as well.

The Scheel’s closest to me has steel case Grendel ammo, which was the lowest cost ammo of all with the exception of some 5.45x39.
Another LGS has both Grendel and 6.8 brass but no factory ammo for either at my last visit.
PPU 6.8 online is reasonably priced given the current market.

I almost grabbed 2 cases of 6.8 SPC Hornady AG last year when everyone was panicking, just to have supply, but it was gone when I went back to Sportman’s.

The last 6.8 SPC I saw on shelves since then was at Cabella’s, Hornady 120gr SST or V-MAX at $30/box.

I was hitting Caballa’s at least 1x/week last year.

Everything has been sporadic for the 2 cartridges looking at factory ammo on the shelves.

The best choice is what you can find and train with regularly. There are pros and cons to each.

Someone said something about projectile shape favoring one over the other and the minuscule differences in diameter.

With a long ogive, there is more opportunity to create larger expansion given the same bullet construction and impact velocity.

The 129gr Nosler Accubond Long Range is probably the cup and core bullet to beat in that respect. It’s very soft but bonded, and expands down to 1300fps.

It’s a great hunting bullet across the barrel length choices, even down into the PDW-sized really short guns.

Here are some figures from Precision Firearms on velocities obtained with shorter barrels:

7.5 Bartlien at 100 Yards. Groups averaged 1.5 Inches 2040 FPS 123 Match King
8.5 Bartlien at 100 Yards. Groups Averaged 1.4 Inches 2100 FPS 123 Match King
10.5 Bartlien at 100 Yards. Groups averaged .9 Inches 2200 FPS 123 Match King
12.5 Lilja Blank Chambered by PF at 100 Yards. Groups .75 2300 FPS 123 Match King
14.5 Lilja Blank Chambered by PF at 100 Yards. Groups .5 2350 FPS 123 Match King
14.5 Krieger at 100 Yards. Groups averaged .38 2375 FPS 123 MatchKing

I have everything from 22” down to 10.5”. I’ve been thinking about an 8.5” suppressed for a while now.

A 10.5” Grendel already out-performs a 20” .30-30 Winchester, having more energy at 400yds than the .30-30 does at 200yds.
Same with 16.3” 7.62x39 vs 10.5” Grendel. 10.5” exceeds it with the same bullet weight by 100yds, and almost doubles the supersonic reach.

I’ve severed cinder blocks with 16” Grendel just using 123gr SMK, not even bonded or solids, at 50yds, whereas a 5.56 would punch a tiny hole in them.

Running the 8.5” Grendel through an internal ballistics model built for 6.5 Grendel that has consistently proven to be within 8fps for me in real-world tests, with the 129gr ABLR, you would have surprising performance from it using a 35yd zero.

2054fps mv
1.7” high at 100yds 1045 ft-lbs
-3.6” at 200yds with 901 ft-lbs with 1774fps impact speed, 474fps over the threshold of 1300.