Please see the link below.  I know there's some cross pollination between 6.8 and arfcom but I thought I'd post the link for those who don't visit both boards.


http://68forums.com/forums/showthread.php?20601-Ruger-chamber-info-Gathering-thread

When they spoke to me about doing a 6.8 I told them they were crazy not to do a SPC II chamber....

but what do I know....

Thanks for the link , Melvin.

I've always liked the idea of a 6.8 mini , but I won't do it until they upgrade .It would be so much like a .276 Pedersen Garand .

Interesting read.

(I'd also be interested in a Grendel Mini , Gunwritr!)

You are going to see people claiming that the SAAMI and SPCII chambers  make a difference of about 1500 PSI.  There have been tests done with calibrated SAAMI spec control ammo, and I have no reason to disbelieve the results but I have personally seen much higher pressure generated in chambers which either had incorrect specs, or those which were "tight" to begin with.  The longer throat of the SPCII does decrease pressure and allows for hotter loads, but there are several other determining factors, like the barrel material, presence or absence of chrome, and rifling design.  IMO, you are much more likely to see a tight chamber which shows pressure earlier if it is SAAMI spec.

I have also seen SAAMI chambered, SS WOA barrels that handled my hottest handloads, and we thought that this must have been explained by the absence of chrome, and the superior riling design.  We disclosed this during our pressure tests in 2008, because we were looking for objective indicators of the differences we saw between the SAAMI and SPCII chambers, and the rifling profile / twist most commonly associated with each.   People should also note that the "DMR" chamber had only .080" increased freebore, but had a more gentle cone angle and was often paired with 12 twist and 3 grooves.  I have fired almost every branded 6.8 barrel ever manufactured, and I have never seen anything else handle pressure like those 12 twist, 3 groove barrels.  SO, the point is that there are many factors that go into the overall peak pressures, both at the chamber and at the gas port, and you cannot predict a barrel's pressure handling solely based upon the chamber.  Remember Ko-Tonics barrels that were excessively chromed.  They had SPCII chambers but too tight a bore.

The SPCII allows for a margin of error you won't get with the SAAMI chamber.  If there is 30-50 FPS to be gained with certain powders, and there is no disadvantage to the longer leade, then why would anyone in their right mind stick with SAAMI and 10 twist?

We all know the answer:  Legal liability.   I truly hope that Ruger and Remington switch over to the SPCII chamber.  Very few buyers want a SAAMI chamber anymore, and since there is NO disadvantage to the longer freebore, then any edge we can get in velocity or reduced pressure is worthwhile.

How does temperature effect chamber pressure in a SPCII chamber?  I seem to recall hearing somewhere that the SPCII chamber showed dangerous pressure spikes in sub-zero weather.  

Personally, I'd be interested in the new chamber as a means to reduce chamber pressure with factory ammo rather than something that allows for hot handloads.  Not that I am against reloading or wouldn't test out the new chamber to see what it'll do.  But I blew a primer with a SAAMI chamber and "normal" ammo in a carbine class.  This loose primer wound up getting caught between the bolt carrier and charging handle.  That rifle was locked up tight.

Here are two links to the same post about what the measured pressure differences are between the 6.8 SPC-II and 6.8 SPC SAAMI chambers.

They shut down the discussion on the 68fourm in less than 3 hours.  There was no name calling or profanity used in the post. I guess they 68 fans did not want to discuss/confront real data. They even turned on the favorite guru DocGKR.


68fourm:  The-truth-about-6.8-SPC-SAAMI-vs-SPC-II.

The same information was also posted on snipershide.  I did not seem to get much traction there.  

Snipershide:  The-truth-about-6.8-SPC-SAAMI-vs-SPC-II.

The comparison is not apples to apples, if that were the case we would still be using that shotty remy ammo. Listen to the guys who know and have fixed this round, where as rem fudged it up to almost extinction. Rsilvers has an agenda and it is not promoting the SPCII chamber.

That thread does seem to have been closed rather quickly. Especially when compared to some of the other nonsense that gets posted over there. Too bad. It would be nice to have an intelligent and honest debate about Western's findings.

Maybe the 6.8 sucks no matter what you do to the chamber.....

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The better chamber isn't just for hand loaders, it has caught the attention of major ammo compaines like SSA and WC. Now why would they produce hotter ammo if there is no difference in SAMMI and SPCII offerings? The argument just doesn't add up.....

Because that's only part of the story, I have been dealing with Johan from AA for a while now(over a year) testing the 6.8 with their AA2200 powder and have data that shows over  4K psi pressure drop between the SAAMI chamber and the loads made for a spc-II chamber, like HTR has said it's more than just the free bore alone and I don't care to discuss it with people that don't know what they are talking about like rsliver which started that stupid "truth about the spc-II" thread.

Do you really think companies like Armalite, Bushmaster, DPMS, CMMG, and a whole list of others bothered making the change for only 1K PSI and 20 fps difference, factory ammo from the same box has a much larger variation than that and it's almost impossible to measure 1K PSI when that's only .2gr of powder and the ammo being tested varies more than that.

SSA is the ones that had the spc-II reamers made for their Combat ammo they use to make and I assure you it made more than 1K psi difference, you cant even distinguish a 1K psi difference yet their ammo was safe in spc-II but unsafe in SAAMI, that's way more than 1K psi difference regardless what one powder company says with no actual data from their test to prove it. We don't even know for sure if they used the proper reamer, there are several out there that have way to short of a forcing cone and a very steep cone angle, this would cause a rise in pressure instead of dropping it or at least prevent you from seeing the true pressure drop and many companies have used these reamers without ever knowing it.

Regardless, if you don't think it makes a difference then just buy a SAAMI chamber but don't come crying when it keeps popping primers even though it's only 1K psi more pressure.

It will never suck as bad as the Grendel and thats all that matters

It was locked for beating a dead horse, it has been discussed and those who know the round have proven much better results. Nonsense? LOL, you might want to remember what site you are on now.

Forgive me. I don't know who rsilvers is or what his connection to the 6.8 cartridge is.

With that said, what could he have to gain from wanting to stick to an inferior chamber?

Posted Via AR15.Com Mobile

I believe he works for Remington and they have yet to admit their screw up, while other ammo makers have passed them in the race.

LOL!

Tell you what, you pick your 6.8's and I'll pick my Grendels, and we'll shoot from 50-1200 yards, and see what the results are.

You design half the stages, and I'll design half the stages...

How about that?

Better yet....David Fortier likes both, and has access to both. He could probably make an article out of it. We'll design the stages and let him shoot them and let the results fall where they may...How's that?

David, you up for that?

That way there is no difference in the shooter, only the rifles.

I'll be at Butner around the end of Oct. Not sure if I will be shooting my ARP or LTR in 6.8. Come on down with those Gs.

The article from David sounds good, as long as it doesn't turn out like that steaming pile Towsley did. A comparison with a non biased shooter would be nice.

As an aside, what does Barrett use for its chamber?

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I think that the 468 used Barrett's own chamber, which was very similar to the original Murray chamber.



The REC-7, in 6.8, uses the SPCII.



 

If Ruger steps up to the SPC II that'd be great....as long as they go with a 1:11 - 1:12 twist rate

I'd be down for a light wt 16" bolt gun

It will be interesting to see how this all plays out. But I'd imagine a twist change would go hand-in-hand with a new chamber.

Posted Via AR15.Com Mobile

Wish I could shoot Butner, I'm in the REAL Washington, the one on the west coast!

It would be interesting to see David do this kind of a shootout!

hopefully

He may work for a company that is promoting the 300 AAC, which also happens to own Remington.

Or....he may have DESIGNED the .300 AAC...........



ETA: I am very impressed by Docs posting, that he came out and said that.

why?  twist isn't even top 3 to look for when buying 6.8 and has no affect on accuracy.  rifling, throat, chamber, barrel are more important than 1/10-1/12 twist

now that is a $hitty round......talk about being the middle child......

It's very obvious just exactly what the agenda is.

Refuting the SPCII means the parent company didn't make a mistake, and therefore, can't be wrong about the .300 BO Whisper copy, either  Oh, yeah, it's just a copy, like the .264 LBC. is still a 6.5Grendel.

Lots of references to the .300 Whisper ignore the simple fact shooters submitted the .30 X .223 wildcat back at the first Soldier of Fortune shoot, where competitors were attempting to conform to the written rules and get around the Main Battle Rifle bias. Didn't work out, the organizers just denied them anyway. It was likely even older than that, but no one is saying.

That was in the '80's, the .30x.223  has been around for over 30 years JD notwithstanding, and it still hasn't got traction. Look at what it is, small case, not much powder, pushing a large cross sectional area. It does exactly what the 6.8 does compared to the 6.5, and more of it - gets a lot of power fast from the charge, moves out rapidly for a short barrel length, and loses it even quicker than 6.8SPC. Of all the things a 6.5 fan would dog the 6.8 about, the .300 BO does it more. It's no way ever a 600m high BC capable cartridge.

it's a no brainer, the paid employee reports the target has poor performance, stirs up debate, and makes noise about his factory design.

The REAL point is - lacking the ballistics or ability to go against any other cartridge, once again, the 6.8SPC is the target - because the shooting public understands it's performance and made it the #1 alternate. If you're "as good as" it is, then that means something.

Marketing by tearing down the other guy and claiming your product is the "just as good" is basically admitting it's not better. Especially cherry picking the worst of what is offered - SOMETHING THE SHOOTING COMMUNITY KNOWS WAS SCREWED UP, THE 6.8 SAMMI.

You want to prove something, don't kick the rock star's midget. Grab a guitar and play. You can either beat the devil, or you can't. Problem is, they bet their soul on it, and they will do anything to win.

Right there, guess what, the devil wins.

Moral of the story, set your target up to be the loser. 5.56 basically can't compare with a cartridge designed to be 40% better. So, 6.8SPC - which targeted the 5.56, is always "better." More power, runs from the same length barrel, and as it gets developed, runs just as fast with a bigger bullet, from a 6" shorter barrel, as 5.56 did.

You want to beat that, build a 7mmX45 or something already. But whoops, it wont' fit the AR mag well. Bummer. THAT"s the agenda - have the best cartridge for the next fad rifle, something just like what the 1911 did in the late eighties thru nineties. Massive growth market with huge profit potential

it's probably too late, all the new calibers really just fragment it and cut sales for everyone. The public has already made 6.8SPC the #1 alternate. More cartridges limited by the AR mag well can only skew the performance to one side or the other,  big bullets or streamlined ones, slow or fast. The middle ground of best all around EFFECTIVE LIVE TARGET performance is 6.8SPC. And since hunting is what really drives sales in the rifle market, the 6.8 will continue to be all it can be in AR sales.

It's all about where the bullet hits the bone, charts and graphs don't field dress animals.

It was locked due to beating a dead horse. The differences have already been done to death with a trace pressure system by Harrison Beene and Tim W. For those that want real answers rather than fluff from a guy that is threatened directly by the success of the 6.8 here you go. The differences are far greater than 1500psi.

{[PDF]
á 6.8áPerformanceáTestingáReportá}

If someone could make that hot for me I would love it. I seem to have a problem with that.

http://m.b5z.net/i/u/6132121/i/6.8_20SPC_20Performance_20Testing_20Report_1_.pdf

Well that just concludes Rslivers so called test, LOL.

Warshington, eh? I'm looking forward to the shoot and will give my 6.8s some good testing from long ranges.

This information completely confuses me. I've been willing to accept the claims of the SPCII chamber boosters for years, especially with the testing reports from those using supposedly advanced equipment. Even leaving out Rsilvers information, when DocGKR and Johan Loubser, neither who have anything to gain from knocking the 6.8 SPCII, point out that to their knowledge no testing has indicated an advantage to the SPCII chamber, something throws flags all over the place.

DocGKR has been a big 6.8 supporter for years, yet he states he is unaware of ANY testing which validates the claims of the SPCII supporters. Johan Loubser's company makes powder, not rifles. He couldn't care less what chamber gets used, as long as his powder is in it.

Yet both are willing to go out on a limb and say they saw no significant differences, reinforcing what Rsilvers said. DocGKR even says that to his knowledge, "The information Mr. Silvers has posted is the factual truth. Every professional ballistics facility, including USG, foreign military, and Industry, that I am aware of that has tested 6.8 SPC vs. 6.8 SPCII using industry standard equipment has reported only a 1000-1500 psi change."

I have NO dog in this fight, I personally like the Grendel, but it seems like there is a group of 6.8 boosters who refuse to acknowledge the possibility that what they have been told may be in error. When you have multiple sources of information that tests a hypothesis, and ONE of those sources is grossly out of line with the rest, it would seem that you would have to look at that source with skepticism. Instead, it appears from this thread that people will accept that one source, and discount all others. That is generally known as fanaticism in the real world, and its a dangerous place to be in scientific circles.

I'm not enough of a scientist and statistician to figure out why there are such gross differences, especially without access to all the data, so we have to take the word of Dr. Roberts and Mr. Loubser, (again discounting Mr. Silvers simply because some here believe he is biased due to his relationship with Remington). BUT...Dr. Roberts and Mr. Loubser have well known reputations. They are acknowledged experts. (Many will recognize that Dr. Roberts and I have not always agreed on things.)

BUT someone might want to start the process of getting all the information in one place and evaluating it. Some of that information might require FOI requests, even.

All of that sounds great until you think about it for a minute. 1000-1500 psi would not be enough to warrant that SSA's Tac loads and Wilson Combat's ammo come with a warning that they be used in spec II chambers. Good to Go Ammo is getting ready to load for Spc II chambers as we speak and you will have to tell them that you understand and you have a spec II chamber in order to buy it for liability reasons. Silvers states that the difference is not enough to pop primers or show signs of high pressures yet we know that statement to be false. SSA and others will show signs of excess and pop primers in SAAMI chambers. That is real world evidence.

Over the years I have spoken with engineers at a number of ammunition and firearm companies about this.
They ALL stated they believed people were handloading the 6.8 SPC to excessively high pressures in search of velocity.

Yet how often do you hear of a 6.8 gun going Ka-boom?

Think about it......

It appears it isn't Rsilvers evidence alone, but the evidence of AA/Ramshot powders, and "Every professional ballistics facility, including USG, foreign military, and Industry, that I am aware of that has tested 6.8 SPC vs. 6.8 SPCII using industry standard equipment has reported only a 1000-1500 psi change." per Dr. Roberts.

Real world evidence, unless documented in controlled environments, is known as "anecdotal" in the scientific community.

Something is seriously wrong here, but.....

I would rather shoot Silver State combat loads through my Noveske 6.8 or my old Kotonics with their chambers and twist rates than through the SPC I with it's twist rate....

Someone has to push the envelope or we'd all still be chucking rocks...damn the lawyers full speed ahead....

To bwaites, you raise a good question and while I have great respect for Doc, the findings he is claiming true just don't add up. We use the SPCII chamber for higher pressure/velocity and get a higher pressure safer than what would be considered crazy for a SAMMI chamber. The numbers are greater than 200fps and 1500psi as found by TIm, H and the others in the real tests. Anything from Remington is skewed since they have not admitted they fucked up the first time. I will not accept anything from them test wise, hell they even used that dinosaur ammo for the test.

You along with others feel the same, the original SAMMI chamber is old news and needs to be replaced to stop the confusion.

Yup, the 200 FPS and 1500 psi doesn't hold water.

346ci, I'm willing to throw out Rsilvers input, due to so many here who are suspicious. That doesn't impugn either DocGKR's and Johan Loubsers information, though.

As DocGKR points out, he apparently has reviewed information from MANY sources and it all confirms what Rsilvers says. In combination with what Johan Loubser states, it would appear that there are many points of data which are in agreement about the results.

Even disregarding Rsilvers statements, the confirmation of those statements from multiple other sources means that the conflicting data needs to be reexamined and the testing repeated and confirmed. That is the scientific method.

In the orignal configuration tested by the Army, wasn't there a perfect storm of screw-ups that caused popped primers (gathered from various threads both here and 68forums)?
1.  Original Hornaday ammo not to print (bullet related)
2.  80 degree cone angle shaving copper, causing pressure problems after a few rounds (this is the big error in the Remington drawings submitted to SAAMI)
3.  Short leade (0.050")  SPCII has 0.100"
4.  6 groove rifling (3 to 5 showed less pressure)
5.  1 in 10 twist (1 in 11 to 1 in 12 showed lower pressure)

So, I am wondering if all these factors came together to cause poor performance way back when it was tested by the Army.
There may be some synergy (not a statistical term) involved.....simlpy put, the sum of the individual minor changes have less effect than all the changes taken together. The whole outperforms the sum of the individual parts.  Perhaps that is why the data on chamber alone (SPCI v. SPCII) didn't show much difference.  The chamber change is just one of many improvements since Remington's release.  When you add up the 5 small changes, then you can load 4k higher pressure and get another 200 fps & +75 yards of useful killing range.  Also, most reloaders like small primers since it gives a little more room for more powder.

The "real" tests? Those 2008 tests were done in an extremely unscientific manner, comparing a few rifles of different makes, each with different combinations of chambers, barrel lengths and rifling twists. While Tim, H, et al, deserve to be applauded for their effort, the 2008 tests simply did not –– and could not –– give definitive results due to too many variables.

To get a truly definitive answer as to how much difference SPCII makes compared to the SAAMI chamber, it'd be necessary to use a methodology like that described by rsilvers in the locked thread, except using both SAAMI and SPCII (or even just SPCII) ammo:

- Test with SAAMI chamber and 1:10 twist; ream chamber to SPCII, and repeat test.

- Test with SAAMI chamber and 1:11 twist; ream chamber to SPCII, and repeat test.

- Test with SAAMI chamber and 1:12 twist; ream chamber to SPCII, and repeat test.

That way, it could be determined to what degree the chamber configuration and rifling twist has on chamber pressure.

you would also want to do this with different manufacturers due to chamber, rifling, and throat differences.  for instance, ssa developed the hotter combat loads (vs today's tac loads) with lwrc's 1/10 twist (yes lwrc combo of rifling, twist etc etc is superior to other 1/10 and 1/11 manufactures) whereas other 1/10s like first run noveske had issues with the pressure of these rounds.

you need to do a complete apples to apples....but, i agree

oh and let's not forget that even though the 3-6 rifling has differences, these differences can be mitigated with some of the superior materials and process of making said barrels.  for instance, the harder and better land groove the barrel, the less the issue of 3,4,5,or 6 groove becomes.

Not exactly the number of lands that make the difference it is the land to groove ratio which changes the bore area and other factors in the bore. Chrome lining adds to the surface making the bore area smaller and creating more pressure.

And in order to get statistically significant data you would have to do it with LOTS of rounds. Think hundreds!

Do not forget temperature.



-40°C to +50°C



 

+65C would be much better