The truth about 6.8 SPC SAAMI vs SPC-II

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The truth about 6.8 SPC SAAMI vs SPC-II

Post by silencertalk »

The actual difference between 6.8 SPC-II and 6.8 SPC SAAMI is at most about 30 fps.

A number of tests have been done in private by the industry, and I got permission to make one public. It backs up the other data from multiple carefully done studies.

----------------------------------


From: Robert Silvers
Sent: Thursday, July 14, 2011 5:06 PM
To: Johan Loubser
Subject: Re: Western Powders Ballistic lab

Johan,

Have you ever done a test where you take a 6.8 SPC SAAMI test barrel, measure velocity and pressure, then ream the same barrel to 6.8 SPC-II - and add more powder to match the pressure of the previous test, and then see how much extra velocity there is?

Robert.

----------------------------------

Robert,
Yes we did exactly that and the difference was negligible as to be ignored ca 20-30Fps and <1000Psi.
I know there is a lot of claims out there regarding this.
Some apply the effects of other calibers (such as the 223Rem) with completely different expansion ratios to the 6.8SPC.
The 6.98Spc is not sensitive to the slight changes in dimensions between the std and SPEC II.

Regards
Johan Loubser
Ballistician
Ramshot.Accurate.Powders

----------------------------------

Robert,
Example is that with SAAMI reference ammunition we got a difference of Pressure: -2.5%/-1200Psi and -19Fps
If one consider that is equal or less than one standard deviation I consider it negligible.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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They seem to really like you over there. :lol:
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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I am surprised they can't follow the results of the test and why it is valid - but realistically that may be asking too much. It is a science-thing.

The differences in barrel performance they speak of do exist, but they are due to larger bores - and not twist or chamber drawings - and so they would never be part of a pressure comparison test. People can take advantage of this in their own barrel with hand loads, but no ammo company - even one making 6.8 SPC-II ammo, could ever count on it - even if a new spec were standardized.

Small differences in twist is not a factor in velocity/pressure. This has been proven by the Govt. There is no significant difference in pressure going from 1:12 to 1:7 twist in 5.56mm, for example. And there is no significant difference going from 1:12 to 1:8 for 308. And going from 1:10 to 1:11 twist will likewise not raise the velocity potential of 6.8 SPC-II.

If they don't believe me, and they don't believe the Ballistics Engineer, then at least consider what DocGKR said (I assume we all know he is a professional wound ballistics expert and gives lectures to the military):

"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."

This is actually settled among the professionals in the ammo and ballistics industry, and I was just providing to the public what was already known in R&D labs.

Instead of a sticky it gets locked - seemingly for heresy.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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Yea, DocGKR isn't a big fan of the 5.7x28 either, which makes him a poopie head to people who think the 5.7 is some Death Ray. (It's a modernized 22 Hornet, get over yourselves.)
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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What do you mean either?

DocGKR is a huge 6.8 fan.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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silencertalk wrote:What do you mean either?

DocGKR is a huge 6.8 fan.
But he is not a fan of the SPC-II as he's pointed out, as you have, that it is nothing but hype.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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Crosshair wrote:
silencertalk wrote:What do you mean either?

DocGKR is a huge 6.8 fan.
But he is not a fan of the SPC-II as he's pointed out, as you have, that it is nothing but hype.
I think he is a fan of SPC-II. If you search back on M4C, you can see him suggesting SPC-II with 1:11 twist.

But he is also open to evidence, and it seems like in the last year he has seen the real data, and his new position is that he will take any extra performance he can get but is happy with the 2650 fps attainable by regular 6.8 SPC.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

Post by silencertalk »

http://www.ar15.com/forums/t_3_121/5423 ... amber.html
EWP wrote:I don't care to discuss it with people that don't know what they are talking about like rsliver
Everyone who has successfully launched a cartridge into SAAMI raise your hand.
EWP wrote: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
Sounds like he used an out of spec SAAMI chamber compared to an oversized SPC-II chamber. If a test is conducted properly - with minimum size reamers and bores for each, then there is a 1000-1500 psi difference. This has been proven several times, and no test has proven otherwise.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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346ci wrote:It was locked for beating a dead horse, it has been discussed and those who know the round have proven much better results.
Actually this is the first public data of what has been known by experts for years. I have been unable to publish this kind of data until I secured permission. The tests he is referring to which have 'proven much better results' did not control variables such as bore cross sectional area and chamber dimensions and did not use professional grade pressure measurement equipment such as conformal sensors.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

Post by silencertalk »

Melvin_Johnson wrote: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?
Or for that matter, what would a powder company gain?
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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6.8 forums has a poll, and people voted to keep the thread closed.

http://68forums.com/forums/showthread.p ... -II-thread
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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Re: The truth about 6.8 SPC SAAMI vs SPC-II

Post by 82nd airborne »

The advantage of the SPCII isnt about velocity at all really.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

Post by Crosshair »

Holy crap. At least 9mm vs 45 threads at least have some decent science and argumentation in them.

I love this post
He's just upset, because the 6.8spcII outperforms the 300 blackout in accuracy and ballistics.
Talk about pulling info out of your bum. I may poke fun at the 300 Blackout as a reinventing of the 7.62x39 by people who greatly enjoy overpaying for stuff, but even I know that statement is crap.

Accuracy is a function of ammunition quality and rifle quality. 7.62x39 Ruger, CZ, and Savage bolt guns can shoot nice groups when fed quality ammo.

As far as ballistics, that depends on what you are trying to do. Tell the 6.8 fans to load a 150 grain spitzer bullet into their 6.8 and see what happens.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

Post by silencertalk »

Thank you Dr. Roberts.
DocGKR wrote:Nonetheless, the difference in SPC vs. SPCII is truly not as dramatic as many in the 6.8 mm community believe nor is it the main reason that early 6.8 development suffered. I suspect the main roadblock to widespread early military 6.8 mm adoption was the bad lot of Hornady bullets with a non-legal tip design that caused 6.8 mm to loose JAG certification, not any issue of SPC vs. SPCII. In addition, a lot of 6.8mm problems have been due to tolerance stacking--numerous early commercial weapons had extremely small chambers and tight bores that frequently resulted in overpressure issues. Certainly a proper SPCII rifle offers a substantial improvement over such situations. Conversely, a SAAMI spec rifle on the looser end of tolerances is not going to be dramatically different than a SPCII rifle.

...

I suspect there are a lot of folks misunderstanding both the pressure information that was presented and Mr. Silver's motivations.

...

Mr. Silvers is widely respected and consulted by quite a few military, as well as Federal LE organizations. In my experience, he has consistently been quite positive in his comments to industry and the USG regarding 6.8mm and I have observed him working behind the scenes trying to assist 6.8mm development and help 6.8mm improve. It is quite appalling that many individuals here seem to misinterpret his comments and to want to ridicule his efforts, especially in light of all he is doing to aid our military service members and LE personnel. Many other well qualified individuals have been driven off of this forum after receiving similar treatment, it is truly unfortunate.
http://68forums.com/forums/showthread.p ... ead/page13
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

Post by silencertalk »

I got an email from Art of SSA after he read the locked thread on 68forums.

Art said that he has a lot of 6.8 rifles, and he has noticed some of them cannot handle 50,000 psi, while others can handle 55,000+ psi. This is consistant with what the 'real world results' people are saying - that when you look at rifles in the wild from different makers, there is a difference of up to 5,000 psi.

He also said that he cannot disagree with my statement that there is only a 1000-1500 psi difference and less than a 30 fps increase comparing SAAMI vs Spec-II chambers in a 24 inch test barrel.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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Thak you again Dr. Roberts.
DocGKR wrote:I am extremely disappointed in the shrill myopic histrionics being displayed by some posters. I consider Mr. Silvers a valued ally in the quest to improve our Nation's military and LE weapons capabilities. Despite many of your ignorant comments, Mr. Silvers has ALWAYS been very helpful in aiding 6.8mm's progress, as well as that of other important weapons programs. Keep in mind that there are numerous factors at play in achieving either increased velocity or reduced pressures, as this requires a balancing of the right powder, well designed projectile, correct chamber, appropriate twist rate and rifling characteristics, proper port size and port location to name just a few of the factors. The designer of the 6.8mm has clearly stated that for military and LE use, it is very important to keep pressures below 55,000 psi. Hotter ammo that works for a competition shooter or hunter who may re-barrel or replace their weapon after perhaps as little as 5000 rounds in some cases is far different from SOF or SWAT personnel who might shoot 5000 rds in a week's training. Mr. Silvers reported accurately on pressure testing conducted by reputable facilities--other combinations may result in different findings. Get over it and start behaving like adults.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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http://www.ar15.com/forums/t_3_121/5423 ... tml/page=2
stanc wrote: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.
It is good thinking - but we already know that rifling twist has little to no measurable effect on chamber pressure (which is why twist rate is optional in the SAAMI specs). One could test it to settle the public debate, but to SAAMI member companies, they already know the answer.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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Not to argue, but to find an answer; if/since twist-rate doesn't affect pressure-and/or-velocity, then why don't more rifle barrels come in slightly more aggressive twist rates? It seems that there is always the issue of "does-this-twist-rate-stabilize-this-subsonic-load?" That could be averted if all barrels were made 10-15% more aggressive... so that a 1-in-10 becomes a 1-in-9, or a 1-in-8.5... and so on.

Also, are you asserting that twist-rate doesn't affect velocity, or that it doesn't have any meaningful correlation on velocity (ignoring outlandish, 28-turns-per-inch rifling).

Finally, what are those people upset about? Do they view your posted data as an assault on the 6.8 II because you are a 300-BLK proponent? Or is this merely defending their purchase, and by extension, their stance on the 6.8 II issue?

Finally (the second finally), is the minor variances in the chamber dimensions from one rifle to the next where the 'magic' is as to why some handloaders are experiencing the capability of over-loading the 6.8 II in order to achieve its fantastic gains? Am I reading that correctly? If so, then I feel that at a certain, undefined point, what they're doing is essentially wildcatting, because that hotter-than-factory-load that works in their rifle, may pop a primer in their neighbor's, slightly tighter, but still-within-the-window-of-factory-tolerances. Is that statement also correct?


I own a .17 HMR, two .22s, and two 9mms. I have a Kel-Tec RFB on order. I have no 5.56 NATO, 6.5 Grendel, 6.8 SPC, nor 6.8 SPC II. I say that to demonstrate that I have no 'dog in the fight'. Not an attack, just a question; why did you post that data on the 6.8 forum? It was good reading, and the responses are psuedo-typical of the gun crowd --- a field where, frankly, not a lot of data is available for what happens in that microsecond in the chamber, or at the point of impact, for that matter. People end up with a "lucky-socks-that-won-the-game" mentality, and don't change from the .30-06 their great-grandpa used, because it worked then, and each subsequent time. I get the haze of voodoo that surrounds hyped and mythical cartridges (and try not to fall victim to it myself). Not attacking, and not saying you shouldn't have, but still, why did you post that there?
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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TROOPER wrote:Not to argue, but to find an answer; if/since twist-rate doesn't affect pressure-and/or-velocity, then why don't more rifle barrels come in slightly more aggressive twist rates? It seems that there is always the issue of "does-this-twist-rate-stabilize-this-subsonic-load?" That could be averted if all barrels were made 10-15% more aggressive... so that a 1-in-10 becomes a 1-in-9, or a 1-in-8.5... and so on.
I have said that 1:8 is the new 1:10 for 308, and AAC sells 1:8 twist 308 barrels. I know of a govt lab which tested that twist and found no downside in pressure/velocity.

So why is it not done more? Many believe it harms accuracy to spin more than needed. Do I believe that? I believe it sometimes does, and I would not do it on a benchrest rifle, but I would on a combat rifle and even a sniper rifle.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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TROOPER wrote:Also, are you asserting that twist-rate doesn't affect velocity, or that it doesn't have any meaningful correlation on velocity (ignoring outlandish, 28-turns-per-inch rifling).
I am saying that if you get two barrels that are identical in every way, including bore cross-sectional area, but differing in twist by one being 1:12 and the other being 1:8, there will be no measurable difference in velocity or pressure. They must differ a little, but that amount is below the ability of the equipment to detect.

For example, in a govt test, they saw the 1:8 barrel as 4 fps slower than the 1:12 barrel, but that 4fps was within the error of their chronograph. This means they could shoot twice through the same barrel and see more than a 4 fps difference - so they called it the same.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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TROOPER wrote:Finally, what are those people upset about? Do they view your posted data as an assault on the 6.8 II because you are a 300-BLK proponent? Or is this merely defending their purchase, and by extension, their stance on the 6.8 II issue?
Multiple things.

1. They think I am trying to make 6.8 look bad in order to make 300 AAC BLACKOUT more popular, but I don't think this makes it look bad - as under the SAAMI specs you can get good performance. In fact I was trying to help 6.8 by showing people maybe they don't need to argue over specs so much and perhaps can stop scaring people from picking the wrong rifle. For example, Ruger comes out with 6.8 and they are brutalized for picking the standard specs rather than thanked for helping the market.

2. Some guys have more than one rifle, and noticed that the SAAMI rifle cannot be handloaded as fast as their new SPC-II rifle, and the difference may be 200-300 fps - so they "know" I am incorrect. Those guys just don't know the real difference is that their old rifle has a tight bore that is out of spec and is not SAAMI legal to begin with. Their real-world experience does not supersede the controlled variable lab test.

3. Guys see that SSA warns people not to use their "Tactical" loads in SAAMI chambers, and they see this as proof that there cannot be just a 1500 psi difference in the chambers. It is not proof, it is how SSA chose to label their ammo - I assume to filter out some of the early out of spec rifles.

4. They flat out think I am saying that SSA and Wilson ammo is only 30 fps faster than Remington and Hornady ammo. I never said that.

5. It is a religion for them, and I am a heretic. I said something that challenged their belief system.
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Re: The truth about 6.8 SPC SAAMI vs SPC-II

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TROOPER wrote:Finally (the second finally), is the minor variances in the chamber dimensions from one rifle to the next where the 'magic' is as to why some handloaders are experiencing the capability of over-loading the 6.8 II in order to achieve its fantastic gains? Am I reading that correctly? If so, then I feel that at a certain, undefined point, what they're doing is essentially wildcatting, because that hotter-than-factory-load that works in their rifle, may pop a primer in their neighbor's, slightly tighter, but still-within-the-window-of-factory-tolerances. Is that statement also correct?
Yes, they are tuning just for one rifle loads which will not work in other SPC-II rifles.

Production rifle bores need to be allowed to vary from max to min - and a max rifle made on a Monday will differ from a min rifle made on a Friday - even for the same model rifle. Typically, a hammer forging mandrel will be designed to start making barrels at SAAMI max and then they would discard it when the barrels reach SAAMI min.

Because barrels from any given company can range from min to max on the bore and chamber, big ammo companies just develop ammo for the smallest bore cross-sectional area. In other words, their test barrels have minimum chambers and minimum bores, as then they allow for worst case.

So if a SPC-II comes out for real, the factory ammo will not be as hot as what these guys are saying they get in their own rifles with handloads. They have to be loading to proof-round pressure for some of the numbers I saw.
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