Since this has been the point of a certain someone who chooses to try and debate the safety of 6.8SPCII hand loads at above SAAMI pressures of the original 6.8 chamber.
I was working with some loads tonight and referring to Western Powder's load guide.
That is when I noticed something I have known since I started reloading the 6.8SPCII.
I just didn't remember what reliable source I had seen it in.

http://blog.westernpowders.com/WP_LoadSpec_1-23-14.pdf

Please look to page 33
Accurate powders 5744, 1680 and 2200 all list loads over 58,000 psi at an OAL of just 2.26.
With 2200 topping out at 58500 psi.

With the disclaimer that these loads are for both SPC and SPCII chambers.
You see there IS published data for SPCII loads to 58,500 psi.

If this was so unsafe they would not have data published for pressures to that amount.

And, those pressures are from being tested in SAAMI chambers.

Every powder company I have talked to has said that they only pressure test loads in SAAMI chambers, even if the loads list that they are for either.

They test in the SAAMI because it is accepted as standard, and it makes them "lawyer proof" because if the loads are also used in a spec II chamber, the pressures will be dramatically lower.

This had been the answer from every one I have called, and I have called about all of them over the years.

tag

and barrel/rifle makers have mostly gone to SPC II for the lower pressure.The market is saturated enough for the change.

To paraphrase LRRP,; SPC II needs submitted & be done with.

Nosler, Hornady & Federal/ATK can summit the schematics..

Maybe 6.8 GPC or 6.8 NATO () [Just like the .223 & 5.56.]

6.8 NATO for the win

The Accurate Powder data is the very one I have specifically been referring to, which shows that you never stopped and read my posts. I have mentioned it so many times, and every time have been criticized because it also says SPC, as well as SPC II.  Those who have been around for years recall these conversations, and can vouch for this fact.

What people don't get is that pushing the max with one particular gun may work out all well and fine for a few hundred rounds, or even a few thousand.

When you start manufacturing, you now have margins.

Margins in steel quality

Margins in dimensions

Margins in brass

You definitely have margins in reamers.

You can't manufacture to the bravery and stupidity of new reloaders chasing velocity.  This is why we have SAAMI, where they specify the Maximum Average Pressure, Maximum Probable Lot Mean, and Maximum Probable Sample Mean. They also specify the maximum cartridge dims, and minimum chamber dims.  It's a control measure to pin down the ammunition and chambers so that everything can be produced on scale.

58,500psi is the current Maximum Probable Sample Mean for the SAAMI 6.8 Remington SPC.  That's the worst-case sample reading allowable from a lot of ammunition.  Even with the chamber variations, if you purposely load to 58,500psi, you are going to have variations above and below that in your loads.

Many of the common barrel steels will not do well in a fleet test with those pressures.  5.56 NATO M193 will break look-alike AR15's on a regular basis, since a lot of corners are cut in the civilian market.  Now you're talking about running a fatter case with less chamber wall thickness at the same pressures, with less quality control than a TDP gun.  The AR15 was not engineered around 5.56, it was engineered around .222 Remington, which has a SAAMI MAP of 50,000psi.
 
I've done QC work for a pretty sizable rifle maker, and have seen chambers that developed a ring in them.  It's not something you want to happen if you care about the longevity of the rifle. That barrel had to be replaced and barely had any rounds fired through it.

If you are just discovering Accurate Powder's data, what else is there you aren't aware of?  I would suggest doing a lot more research, and less posting unless you're looking for specific questions along the entry-level steps of your quest.

Margins, margins, margins, do you not think this is taken into consideration?
You keep ignoring that 6.8 proof loads are 70,000 psi. To compensate for your margins.

You also ignore they Western Powder loaded those test rounds at 2.26, yet everyone loads SPCII ammo longer, to 2.3 in the case if the SSA 140 Berger.
With a 1:10 twist barrel no less, which is likely a .270 barrel and known to be prone to more pressure spikes than the current 6.8 barrels.


According to you then we could say at the highest loading a 6.5G could take 51,900 psi. As well any sane person would never load to it.
Yet you advise loading the 123 Amax to 2500+ in 16in barrel. Which is it sir, cause your way over 51,900 friend. As well wheres that pressure test no one should load to that without?

And your 16 year old type comments, highly juvenile.

The fact is you have no proof of anything you say, none, zip, no failures of the SPCII chamber you have referenced. Not a single one.
Its like a politicians missing e-mails.

Westerns data shows they are confident any 6.8SPCII barrel can be loaded to 58,500 psi.
Or it wouldn't be in the book. Because their attorneys wouldn't let them otherwise.

Oh, and which barrel maker? I am sure others here would like to know as well.

And the plot thickens

Reading comprehension.  Rifle maker, not barrel maker.  It wasn't a self-loader design either.  NDA's are standard in the industry, so I won't violate them, but it had nothing to do with AR15's or 6.5 Grendel.  Jumping to conclusions isn't helping your shaky position any either.

.222 Remington and the AR15
Again, you are simply not aware of the AR15's history.  .223 Remington and 5.56 NATO did not exist when the AR15 was scaled down by Robert Fremont and Jim Sullivan at ArmaLite in 1957.  They engineered the gun around the .222 Remington, which is a 50,000psi MAP.  This was when the gun was in the prototype stage, and was eventually reamed to allow a longer shoulder with more powder capacity.  That was called the .222 Remington Special, then finally type classified as the 5.56x45.  The pressures went up substantially, and guns started experiencing pitted, cracked, and broken bolts.  The AR15's pressure containment system had to be re-spec'd, but the critical dimensions didn't change.  A series of durability bolt/barrel/bore tests were conducted by the Army and Air Force jointly to address these issues.  The test documentation is now available online.

Bolt alloy and barrel steel, along with hard chrome lining, were some of the main changes added to the TDP as a result.  This is all a matter of record and history of the gun.  If you pick up The Black Rifle, Volume I from Collector Grade Publications, you can learn all about it.

The short story is that pushing the gun to higher pressures caused enough problems that a very specific set of alloys needed to be sourced, inspected, machined, heat-treated, High Pressure Tested, Magnetic Particle Inspected, and shot peened in order to pass the requirements for a military gun.  Even then, 5.56 bolts will still break if the gun isn't built right.  I've broken 5.56 bolts myself.

Now you mention 70,000psi proof loads.  A proof load is a limited test event just to make sure nothing gives.  Nobody would think about running a gun on proof loads, because it's going to yield.  70,000psi proof load (what spec are we talking about, BTW?) does not mean you load cartridges anywhere near that.  There is no industry standard proof load for 6.8 either, since there is no chamber standard.

My 2500fps/123gr load with CFE in the Grendel isn't even 47,000psi.  I think something is falling apart with your ability to read, comprehend what you're reading, and then discuss it. You're approach appears to be throwing as much crap as you can and see what sticks to the wall.  This is grasping at straws.

I need to start sending you a bill for having to go over this again and again.  It's obviously not working.  I explained why margins are important in manufacturing, and why you can't run Maximum Probable Sample Mean as a working pressure.  I'm stating that from a perspective of having done QC for a legitimate rifle manufacturer, as well as having worked with several of the major powder companies in the industry.

God your just never ending.
Mr Twist it.

The barrels proof to 70,000 psi. No one ever said to load a 6.8 SPCII over 60,000 psi, not that I have seen anywhere.
The point is that the chamber does not fail even at 70,000 psi.
The chamber does not fail even even with the muzzle welded shut for that matter.

I am fully aware of the .222 Special, commercially named the .223 and named the 5.56 by the mil.
As well as the dev work with different materials before hard chroming and the use of 158 carpenter bolts.
This is all well and good in the history of the weapon we all love but really has little bearing on this discussion.
Metallurgy in both barrels and bolts has came a long way since then.
Heck by your own admission in 2011 there should not be an AR15 based rifle with anywhere near the bolt head diameter of a 7.62x39
Let alone the case diameter. How do you now recommend those to anyone?

In your constant efforts to downplay the performance of the 6.8 you state the 6.8 should not be loaded to over 53,000 PSI.
Where SAAMI is 55,000 psi, SPCII 58,500 PSI recognized by both Western Powder and Hodgdon .
The reason SAAMI is limited to 55,000 is not the chamber thickness/weakness it is due to the pressure spikes created by using .270 barrel specs.
These spikes could drive the pressure to over 60,000 psi unless the pressure was kept below 55,000 psi.
This is why SAAMI limited the pressure in the early barrels with a .050 leade and a 60:40 land to groove ratio.
SPCII barrels DO NOT exhibit this behavior and are thus not limited to 55,000 psi but able to run 58,500 safely, due to the lack of unpredictable pressure spikes.

Since you have never loaded for the 6.8 or observed over pressure signs when doing so.
When the 6.8SPCII approaches 60,000 psi over pressure signs all show quite rapidly.
Swipe, flattened primers, case head bulge. Its easy to see your over the limit it likes.
It is also very tell tale in the ladders and how the velocity flattens out and accuracy goes away.
There are always 2 accuracy nodes, 1 at a lower pressure and 1 just before max pressure, its a great cartridge to load for.
Very consistently with the 15+ projectiles I load for it.
15+ powders, 15+ projectiles over almost 3 years of loading the 6.8 and 5.56 with over 5000+ rounds loaded and tested in 6.8 alone.
I'm kinda past the amateur stage.
As well you can see how well I shoot, and you don't do that without a bunch of trigger time.
I can actually feel a round that is getting near max pressure before I even look at the brass, my weapon tells me.

This I why I stand up for it and defend it, not because its my "pet". Because it is a very diverse little cartridge, its what the 5.56 should have been.

Again, where is your pressure test data for your over book loadings?
Where's the picture of your pressure test equipment? You certainly must have some pics with it too.

Edit:
Where is your proof of a failed or "ringed" chamber in a 6.8SPCII?
Because all you have presented is opinion and conjecture without a shred of evidence.
No experience loading the cartridge, never owned one.
Perhaps never shot one.
The master of opinions, with nothing to back them.
Just name dropping terms to try and prove your opinions.
Guess what, your opinions are unfounded, because you have no proof.
Yet those of us loading and shooting the 6.8SPCII have proof.
Not one failed chamber or ruined barrel.
Not one.

You can chamber the AR15 in cartridges with diameters exceeding .500" if you want to.  You just have to bring the working pressure down based on engineering principles of pressure containment vessels.

That's where we disagree.  My position comes from a lifetime of dealing with these matters, to include paid positions in quality control for a rifle manufacturer, researching and authoring reloading handbooks, working and consulting with engineers from the various powder companies, and continued development of cartridges that weren't meant to be stuffed into the AR15.

Anyone can see my name on the works I have authored, and anyone with an engineering background in pressure containment can run the numbers for themselves and see.

Why resort to personal attacks in a tech forum, and why as a novice reloader would you post a thread clarifying max pressures on a cartridge with no published industry standard?

If the bolt is the only limiting factor, we should just make a stronger bolt and extension, and load the .458 SOCOM or .50 Beowulf up to 5.56 pressures, right?  Why are those rounds so handicapped by 35,000-38,000psi?

Chamber wall thickness is real.  It can't be ignored so you can get close to .270 Winchester performance in an AR15.  After all, since the Grendel proof load is 67,000psi, I should be able to load her up to around 58,000psi and be fine according to this logic.

If you want proof, learn the math, the materials science, run the numbers.  You don't have to take my word for anything. You're still using primers as a pressure sign indicator, which was identified as a bad practice already in the 1930's by small arms engineers.  This is like a broken record.

interesting thread so far.  I have been looking at the CMMG mutant that several people at my club have just bought.  It is a very interesting concept as it has a bolt that is much much bigger than a regular AR bolt in use in the 5,56 and 6.8.  

The first thing I thought is man they have got to make this in 6.8 with that bolt.  The bolt face is huge but the whole BCG is about normal AR size.  Somebody really needs to redo the AR and come up with the AR 12 concept that has been thrown around for several years on the 6.8 forums.  


Anyone have similar thoughts?

Wow, a troll thread with the opening sentence.

Asking that you show the pressure test system you claim anyone that goes outside loading manual bounds should use is not attacking you.
Its a simple request to back up your claims.

No one ever said chamber wall thickness is a non factor, this is why the 6.8 should not be loaded to 63,000 psi.
Nor has anyone said the 6.8 performs at .270 levels, where did that come from???
Why do you throw stuff into the discussion that is not implied in any manner?

You state a "lifetime" of experience yet just a year 4 years ago you stated the AR15 is to weak for anything over a 5.56, which is it?
This is not attacking as you have often done. This is asking for an explanation of you correcting yourself or changing your feelings on the subject at hand.
Yet you never address any of those questions of you contradicting your self, all the while feigning how your conjectures/opinions must indeed be fact.

I never said I only use primers as an indicator but listed a number of factors every single reloading manual states as pressure indicators.
Are they all wrong?
Yet you elect to pick one part of what I said out and focus on that.
Primer, swipes, case expansion, etc. Primers alone can be unreliable, even give a high pressure indication when there is not high pressure and vice versa.

No published standard in the industry?? Hodgdon and Western Powder have both specified loads pertaining to 6.8SPCII.

You state that the containment vessel/chamber of the 6.8 is unsafe over 53,000, yet the reloading industry says its safe to 58,500.
As well if we use a proof pressure of 70,000 psi for the 6.8 the difference is 11,500 psi to 58,500 psi.
If the Grendel is proofed at 67,000 psi figuring the same math would put the Grendel at 55,500.
However since the containment capability is not linear this is not the case and the G maxes out just below the 52,000 psi mark.
Also in the equation in the G is the bolt strength, which further limits pressures.
So on the subject of math, ya kinda missed it there.

If bolts could be made stronger they would be, such as the adoption of 9310 vs C-158.
Such as the ARP Super Bolt and now many others.
If bolt alone was the only pressure limiter the 6.8 could likely handle a bit more pressure, but its not.


This not a discussion of personal intent. This is about a caliber that is accepted by the industry as being able to run 58,500 psi with hand loads and the associated performance.
While certain parties attempt to diminish these capabilities in any conjurable manner .

Hardly
If this was a thread with no prior reference then sure.
This is clarification of a prior recent technical discussion.

Suuuuure it is.

I quote:
"55,000psi is too much for a .421" case diameter in a .735" nominal minimum chamber at the relief cut, so what is it? I can tell you, it's around 53,000psi considering the yield strength of common steels used for rifle barrels."
http://www.ar15.com/forums/t_3_121/673936_6_8_SPC_at_distance.html&page=2

Question: Do the powder manufacturers specify the operating pressure of a particular cartridge?

Do they say, A) We decree that the operating pressure for the 6.8 SPC II shall be 58,500 psi?

Or does someone else tell them, B) The operating pressure for the 6.8 SPC II is 58,500, so when you are publishing loads for it, do not exceed that specification?

If Option B, then who is it, in this particular case, that told the powder manufacturers that the specification for the 6.8 SPC II was 58,500?

If SAAMI for the regular 6.8 SPC is 55,000 psi, then where did Western Powder get the idea to test BOTH 6.8 SCP and 6.8 SPC II at 58,500? Is this something they up and decide to do of their own accord, for the hell of it, or do they get a specification to work to handed to them from someone else?

Not sure how the powder and published reloading data business works.

LWRC Six8

The biggest problem with 6.8 is that no competent entity in the industry took ownership of it from the start.  It's not an inherently bad cartridge, just a step child with a lot of friends, and a revolving door foster care program that goes from placement to placement.

The first home was dysfunctional, and then it was taken over by Remington, who abused and violated it in the most perverse way, while thinking the State was going to pick up the tab.

Then some drag racers said, "Come with us kid, we'll show you the ride of your life!"

Hodgdon's data lists 53,600psi max pressure

Remington's SAAMI submission lists 55,000psi

Accurate Powder lists 58,500psi

This is a product of bad ownership of the cartridge.  The hunger in the AR15 market for a larger bore, bottle-necked intermediate cartridge has fueled it despite so many critical things going against it.  Who knows if the industry can wrangle this cat in and set a standard.  For someone to come out and say, "This is the standard because I said so, I'm a novice reloader."  does not help things out at all.

The thing is, a SAAMI chamber will reach 55K or 58K as a worst case scenario, well before the Spec II does.

A load that is 55K in a SAAMI chamber, worst case with the old land / groove ratio and all of that, with be 45K in a best case Spec II, like the ARP, with ARP chamber and the melonite , with the poly groove, 5R rifling, correct land / groove ratio. Others will fall somewhere in between, and will average 5k-8K difference. Some SAAMI loads, for instance, tested at 43K in ARP barrels, where they were 53 or 55K off the top of my head in the SAAMI chambered early made barrels.

That difference leaves a lot of room for powder and velocity to increase, before it reaches that same 55K or 58K. Now, take your COAL of 2.26 and move it to 2.30, and again, you have dropped pressures, allowing for a little more before you reach that number again.  

Any load deemed safe for the SAAMI chambers and barrels, are safe in the worst possible situation, and reach those pressures faster.

Spec II loads that would be at 55K-58K in a Spec II gun, especially the higher end like ARP, Bison and few others, would be dangerous in SAAMI chambers, the reverse of the above. Some will be completely safe and in the 55-58K range in the speck II guns, but be 65K and much higher in the SAAMI.

So, any load data book that shows the same load data for both, is testing for a safe load for the worst case, which is the SAAMI spec. That load is safe for both, but in many cases, it isn't even high enough pressure to make a Spec II gun cycle. We are generally near the book max or a couple of grains short in order to make the load cycle reliably.

Yama linked a thread that has the PDF with pressure trace testing showing this.

if there is any doubting of this, it's simple.

Get a side by side test with SSA combat loads, plenty of folks still have some, or any of our hand loads that duplicate them. Load them in a SAAMI gun and even some Spec II guns with the wrong barrel design ( 1/9.5 -1/10  with the wrong L/G ratio), and you will see chewed up brass, blown primers, and some real dangerous stuff. Load that same ammo in a spec II gun from a known good company, which is pretty much all of them now, and it will look damn near new after it's fired.

You can also look at the PDF data from the other thread.

But , if you want real world proof , do the test if you can find an old SAAMI barrel.

There is a reason all of the Tac and combat loads were marked with a warning for spec II only, not for SAAMI.

Or the G2 DPMS.

The main problem the -15s suffer from with these cartridges (small tenon diameter) isn't really adressed by the Six8, even though that's a decent design.

Now from 2013 you said:
"I have conducted tests with the Grendel, pushing lighter 100gr projectiles, and tried to throttle up at close range, and it is more difficult to control than 5.56 all day long, and that's with a 50,000 psi limitation because of the bolt geometry."
So which is it? 52,000 or 50,000 psi? Because when your touting accolades its 52,000, but here its 50,000??? Your 2500 fps AMax load was 52,000 I think you said. Over pressure are we?

The 6.8 a Wildcat?
What does that make the 6.5G with 2 bolts and 5 chambers no one can decide on?
Even you cant decide which pressure it can run!

Apparently Redding feels the same way
Series B
Notice the 6.8 made in every die set they make.
Series D
Oh look who lives here.
"Series D die sets represent obsolete cartridges, wildcats, etc., essentially custom stock. We attempt
to maintain inventory in limited quantities. Consult us for your specific needs."
Limited dies
Yup you should know a wildcat alright.
Bad ownership, ya got that covered as well.

Oh those drag racers, Federal, Hornady, SSA, Nosler, S&B, Barnes, Western Powder  man the nerve of those guys.
Dr Lucci, ARP, Bison, LWRC, Wilson Combat etc. the list goes on.
Ya man, these guys dont know anything do they.

"I vividly remember when we started testing SPCII and DMR chambers and people were nervous about the loads we devised, because they based data on SAAMI. So, once I had access to their factory pressure barrels, I later sent most of my loads to SSA and Barnes to have them pressure tested on more than just trace machinery, and we were usually within 1000 PSI of our trace or predicted levels.
Moreover, that same "limit" was observed, wherein I would not see flattened primers until right around 58,500 PSI.
For those others reading, as you know, swipes still are a little harder to judge because of the propensity for new extractors to gouge the rim, or for over gassed, improperly timed rifles to make them.
When we fired our hotter loads, which approached 60000 PSI, we then started to see both flattened primers with cupping, and some swipes.
I literally just read a thread on the other board where the argument was being made that 6.8 is still a "wildcat" and being hot-rodded to achieve its touted performance.

Sigh...."

58,500 sir, by major manufacturers
I will keep presenting more evidence.

And yours is?
No where to be seen..........








 

First of all, thank you Pavlov for your lengthy response, although I'm mostly just curious how it is that Western Powder settled on 58,500 as their upper pressure limit. Did they come up with that figure themselves, or did they get it from someone? And if from someone, who is that someone?

Yama, I'm interested in your answer to the same question, and, yes, more evidence is cool.

Saw this one and just couldn't help myself.

I am working on finding that out.
Nice valid question friend.

Wow what an enlightening conversation with the man the wrote the reloading guide @ Western Powders
As well as an invitation to come and visit their ballistic department, which I will do soon.

First lets talk about catastrophic failure.
Not gonna see it until over 90,000 psi unless the barrel has a serious metallurgic flaw.
Never seen one working 7 years in that department intentionally pushing barrels until near 100,000psi.
His reply to the difference between a .375 case and a.421 case in the AR-15 chamber?
Big whoopie, exactly what he said.
Not gonna stretch the chamber, not gonna ring the neck.
Barrel relief near the chamber? "Not a factor with the minor difference in chamber diameter."

Chamber ringing, actually neck ringing. Caused by a case that is under filled with powder.
Not gonna happen with a case that is between 85% case fill and light powder compression.
It happens with to fast a powder in cases that are under filled.
The powder lays in the case causing the powder to not be up against the primer.
This causes a secondary pressure spike that in extreme RARE cases has made the neck ring not the chamber.
"Not gonna happen in the 6.8 period", this is why not one case of this happening can be cited.
"There is a lot more than pressure going on, the workable pressure of the 6.8 is really no different than that of the 5.56 as far as containment is concerned"
"You will blow primers out, bulge cases, way before you have any containment issues whatsoever"

I told him the conjectures being presented and asked questions about it all.
"Whoever is saying this stuff is dead wrong" I quote him.
I will leave the part about a certain biological function out although that was stated as well.

He also said the the 6.8 is a surprising little cartridge, and again with the powder requirement it like makes for a very nice internal ballistic package.
"The case fill requirements help with both smooth pressure curves and accuracy".

I also got a not yet released load guide for the new LT30 powder.
With 8 bullets tested from 90 to 140 grains.
LT32 will be in the update as well when done testing.
One of the bullets in the new guide is a 130gr Berger loaded to 2.35. Thats right, what some of us have been doing on our own, dont that just make a guy feel like he might know what hes doing? As well as validate the work some are doing with new powders and the 6.8.

"The pressure of 58,500 is one that seems to be becoming the standard in the SPCII chamber, we have seen no ill effects or any issues whatsoever at that pressure.
We are limited to SAAMI spec of 2.26 OAL when testing for legal reasons. The 6.8 is capable of much more when loaded to 2.3 as you have seen."


Is that good enough for you? Because he elaborated even more.
Now before someone comes along and says I advocate loading to 90,000 psi, not at all.
"But 58,500 even 60,000 is not going to hurt anything." That is a quote.


BluntForceTrauma, thank you, thank you, thank you for asking that question.
It lead me to answers and an invitation.

I also have a new friend, "call me anytime"

Yama, though we have seen testing from several sources for the differences in pressure using the same load data, with the old PDF posted from H and Tim and Chris, and with ART from SSA, and one other I cannot recall offhand, what were his conclusions of the differences between the two?

Secondly, did he say which barrels he tested in either SAAMI or Spec II , and if the books were indeed written for SAAMI, with of course the still usable in the Spec II due to the lower pressures. IN other words, like what I've gotten over the phone, testing a SAAMI barrel, using those loads and pressures, and then knowing that the Spec II will be much lower and safer, leaving it at that because it isn't standard ( SAAMI submitted though it is the standard in the industry )?

Excellent info, Yama. Very informative.

Now, did you happen to ask him why they decided to go with 58,500? Did they do this own their own or were they following someone's specification? If someone else, then who?

The corollary question is why Hodgdon decided to set a limit at 53,600?

What reasons does each give for working to different max pressures?

P.S. Did you happen to ask why he writes that "these loads apply to both 6.8 SPC and SPC II." I'd be interested in hearing his opinion on why there's no difference.

Listing that the loads are for SPC and SPCII does not mean you can get to 58,500 in a SAAMI chamber.
You will hit pressure signs well before that in the early chamber. Due to the .050 leade and earlier barrels.
This is why its limited to 55,000 psi, and the associated spikes with the improper chamber.
They list a starting load which should always be used an worked up for a particular barrel/chamber.
In a SPCII chamber you wont see those same pressure indicators until 58,500+.
Of course depending on the reamer etc.
Also note that loading longer than 2.26 does not mean you can run pressures up to 60,000 in any chamber.
I just allows more powder and potentially more speed and accuracy depending on the barrel/chamber/bullet combo without reaching the pressure as soon.
As well I am not advocating running the pressures over 60,000 psi, not at all.


I will ask more questions when I get over there, in the next week or 2 I will make the trip.

Excellent, and I do have more questions.

You got me curious, so I checked Western's guide for the 6.5 Grendel starting on page 30. The max pressure I found was 51,916.

And so I have the same question: How did they decide on their pressure limit for the 6.5 Grendel?

And if he scoffs at the case head difference of 0.043" between the .223 and the 6.8 (0.378 and 0.421), what does that mean for the 0.020" difference between 6.8 and 6.5 Grendel (0.421 and 0.441)?

All this bickering, for what?

All these problems with over pressure, neck rings, blah blah blah, can be solved with one simple action.

Get a 308. Done deal.

I think we've moved past the bickering and are getting into some interesting info. At least to me.

Its not just pressure in relation to chamber/barrel tenon that is a limiting factor, bolt thrust etc.comes into play.
The G's biggest limiting factor along with the 7.62x39 is the bolt due to the case head size.
Even LR has referenced this in the past.

https://www.ar15.com/archive/topic.html?b=3&f=121&t=585432

I have seen between 50,000 to 52,000 for the G as max. From what LR says 52,000 would be max max for the G.
But again there are other limiting factors.
However pressure of the 6.5G is not the topic or my interest in this thread.
Clarifying the new industry standard for the SPCII short of a SAAMI revision is.

What I'm pondering (and we've known this all along) is that perhaps the pressure limits on the 6.5 Grendel are waaayyyyy too ultra-conservative. I mean, I know this from Bill A. himself. He saw himself specifying limits for the whole system in the worst case scenario, i.e., a fleet of rack-grade military weapons firing mass-produced or steel-case ammo in the extreme cold of Siberia, the barren heat of Saudi Arabia, or the dank jungles of southern China. (My hypotheticals, not his.)

But when we're talking personal, custom sporting arms with good ammo under controlled conditions. . . .

Just listening and thinking and asking questions when something doesn't make sense.

AA limited it to 48,000 to 50,000psi
So at 52,000 you already have your bump.
Bolt thrust still being a major limiting factor from many sources, but you know this.

Now im curios.

If the difference is so small between the 2 cartridges, how come 6.8 would have less bolt thrust than Grendel considering the small differences thus requiring its limits to be noticeably lower than 6.8?

Also, I would love to hear more on BFT's question on 53,500 for 6.8 and why they arrived at that if you can get that info. I am finding this and the last to be informative.

ETA: Spelling.

Here you go:
Bolt Thrust

Its pretty well known the G has a higher bolt thrust ratio then the 5.56 or 6.8 which is higher than the 5.56.
Read away.
The 6.8 does not exhibit the broken bolts that the G does, its all over the Grendel forum and an internet search.
But you guys know this. Also that bolt thrust is a limiting factor more for the G and 7.62x39 (which is one of the 2 G bolts) than the 6.8.
Another reason they based the Hagar off the 30 Rem.

Here are some further numbers on bolt thrust for the comparison at hand.

Bolt thrust generated by common rounds-
5.56-----=6337@58kpsi-----------------------
6.8 -----=7921@58kpsi-----------------------
Grendel=7978@52kpsi------------------
7.62x39=6904@45kpsi
BR------=10542@60kpsi-----------------------
30RAR=10035@55kpsi-------------------

So you can see that at 52,000 psi the 6.5 generates the same bolt thrust as the 6.8 at 58,000 psi.
As well due to the larger case head of the 7.62x39/6.5G/PPC case head the bolt is just inherently weaker.
Pure physics here is it not. :)
This is the limiting factor for the 6.5G vs the ability for the 6.8 to run at a higher pressure.

The 6.8 can run safely to 60,000 psi with a 9310 bolt at which point primers, cupping and swipes will show the limit of the case and case damage will start occurring shortening case life.
The 6.5G is limited to 52,000 psi due to the inherently weaker bolt.

I think my case (pun intended) has been presented with data, industry backing, time tested evidence and no (not one) instance of failure or any indication of damage.
No conjecture, no supposition, no BS.

So why not neck the 6.8 down to 6.5 to run higher BC bullets at equal weight?

Your #'s don't jive with your link....

These last numbers are using the outside diameter of the case head not the inside diameters used in the link.
The resulting difference is still the same.

The Six5 from ARP and the 6.5x6.8 from BHW do just that.

http://ar15barrels.com/tech.shtml

# still don't jive...

Firstly I do not blame any of the anti 6.8 crowd for trying to disprove or diminish what others have taught me and I have validated.
You see I am not a follower, I do research, I make phone calls, I do not take anything lying down or sitting still.
Thankfully, with modern digital media the learning curve of anything is exponentially shorter.
As well if not for the unfounded misinformation I would not have perhaps pursued the quest for knowledge as ferociously.
So thanks for that gents.

As to calculations.
There are a number of ways to do them. In relation to chamber strength and bolt thrust.
They all obviously do not come up with the same numbers.
With bolt thrust do we consider the total chamber as the containment vessel therefore using the whole SQ area case head diameter? Or do we use the internal SQ area of the inner case head and say that it is where the back thrust pressure is generated and applied?
As far as safety is concerned (which has been the topic of all the unfounded allegations) using the outer case head diameter is more conservative.

This is the formula the guy of ar15 barrels is using. It may not be correct in the number of decimals.
=((A20/2)*(A20/2)*3.14)*C20
The bottom line is you use the area of the case inside or out depending on your view then multiply by the pressure.
http://www.basic-mathematics.com/area-of-a-circle-calculator.html
Multiply the area x the pressure to get bolt thrust.
Do the math yourself, you will still find as I just rechecked that the G at 52,000 psi is right with the 6.8 at 58,000 psi.

Focusing on this for lack of finding any other way to dispute that the containment vessel aka chamber of the 6.8 is NOT to weak to handle the pressure of 58,000 to 60,000 psi to me is just another attempt at a distraction.

It has been also subjected that these pressures would not be reliable in combat. But yet with the 6.8 runs in the desert in combat situations in the middle east.
With no reports of failure in very high heat climates in high rate automatic fire. The 6.5G can lay no such claims as no country has adopted its use in their military, not that I have heard of.
But for us here who really cares right? My 6.8 and your 6.5 are never going to see those conditions. Yet it is however a fact. Our military will likely never adopt either, again a fact, because of bureaucracy if for no other reason.
As well it seems to be being overlooked that those gents in the 6.8 community have been using the 6.8 at 58,000 to 60,000 psi since 2008 with NO ill effects.
2008 SPCII test results

This was never intended to be a 6.8 vs 6.5G discussion, although I admit its hard not to considering all the years of bad blood, which was going on long before I came along.

So lets also add what the guy from AR15 barrels added at the bottom since you reference his numbers and calculations.
Sure you wanted to do this?
"I consider 7000 lbs of backthrust as the maxiumum allowable in the AR-15 action.(with the potential for an 8620 bolt I can see this, with a C158 or 9310 its higher)
Note that 7.62x39 AR's are known to eat bolts. (your case head here)
The backthrust calculation would tend to bear this out.
These calculations are VERY basic, completely ignoring all effects of brass thickness and body taper.
Use this as a comparison only, the actual backthrust (if measured) would be affected by many factors that are not being considered here.
Yes I realize that case head diameter is not the effective piston diameter gas acts upon. (this is why some prefer the inner dimension)
This is meant for comparison, the important thing is to compare similar dimensions."

So should we use this as rock solid numbers? I think not.
We should then say what is the truth.
That the 6.5G has a higher bolt thrust and weaker bolt than the 6.8.
Thus dictating it run at a lower pressure irregardless of the chamber strength.


Again I in no way am trying to start a 6.5 vs 6.8 war, they are what they are.
Different strokes for different folks.
But facts and track records are facts and track records.
BS is BS

I could give 2 shits about this cartridge versus that....  

You cut and pasted from another thread  (I can do it too..)

Borrowed an AR Performance post (again) from 6.8 forums...  ( Do you plagiarize all the time?)

Now the 5.56 data there is @ 55000 according to AR15barrels spread sheet (which anyone can download and use BTW)
http://ar15barrels.com/tech.shtml

Using it:
The Grendel .439    52000 = 7867
The SPCII      .421    58000 = 8070

Now you mentioned AR15barrels blurb @ the bottom about 7000 should not be exceeded....

That would hold the 6.8 to 50311psi.



That would make your whole thread and pretty much all the time you spend typing in this forum pointless wouldn't it?  And your right BS is BS

That is a big question for me as well. I guess that is what I want to know why that is for him. Could you ask him when you visit Western? Would be much appreciated. Also, wouldn't something like the superbolts allow for higher pressure for 6.5 considering they are not weaker bolts and seem to be stronger than most bolts on the market?

ETA: Added a question.

The 6.5 superbolt was a solution that worked for many shooters, also for some chamber types there was the big bolt, 800 series I think it was that H made for them, which also worked well. It helped with breakage and allowed a little more pressure to be built, to the extent I don't know, but a ton of people bought them for that reason and it has worked well.

Here's the problem.  The peak of engineering, tool and die making, machining, and metallurgy was in many ways the baby boomer generation.  You had disciplined kids who watched their depression-era grandparents and parents bust their hind ends off to make it through very hard times, two world wars, and then work into an era of prosperity that inherited the war-effort tooling and military-industrial boom that came with the Second World War.

All those engineers, tool and die makers, machinists, and skilled laborers are retired.  Their kids were mostly spoiled rotten brats who saw grandma and grandpa in recliners, mumbling about how things used to be.  Conditioned by television snippet programming, public schooling with a generation of teachers who had almost no classical education, their attention spans dwindled into boderline retardation.

Then they had kids.  These two latest generations are now sitting in the very large shoes of the baby boomers that they don't have the discipline or concern to fill, let alone the intellectual capacity.

For example, several people have called Hodgdon's, and were specifically told that CFE223 is not an appropriate powder for 6.5 Grendel.  This was after Hornady had already published pressure-tested data for it in the 9th Edition, mind you.  Who is correct?  Hodgdon's, or Hornady?  We already know the answer from pretty extensive testing with it that it's one of the most ideal powders for the Grendel.

Also notice how in Yama's account, this particular engineer seems to have an interest in 6.8 SPC.

If anyone would care to run fleet testing like JSOC did, then they would see what problems arise. That fleet testing showed that the rifles they had were unsafe, according to the head engineer that oversaw the tests.

I've seen rung chambers, not necks, but the chamber area where the cartridge side wall is, and it definitely wasn't a half-full case.  You have to understand the context and the scope of knowledge someone has when you are asking them questions, not just take one source's statements at face value and call it good.  I've been in personal contact on a continual basis with the brains of several major companies in this industry for many years now, and they all certainly don't agree with each other.

For example, the advocates of pressure trace will show a secondary pressure event, while those with piezoelectric say it is nonsense.

As you look at those who drank their way through college, and cheated on exams, and can't pass a urinalysis, the problem grows even worse. Throw in the internet, where every novice is an expert after a google search, and people are quick to attack each other's character before doing some more research, and you end up with factions governed by what people want to hear, versus people who accept hard facts.

I call the former the Purple Oompa Loompa generation, where they want their Oompa Loompa NOW daddy!

When speaking with powder manufacturing companies, keep in mind that they have one particular area where they specialize in.

Ammunition-manufacturing companies, especially the big ones, will burn through many barrels just in lot-testing of existing production lots.  In a recent discussion with an engineer from one of the biggest ammunition makers in the world, we had this talk about the generational changes that have brought in a lot of incompetent employees in critical areas of the departments.  It's a very real problem.  Popularity contests often win over engineering and logic.  It's pretty sad to watch the decline really, especially given the potential boom of technology that was handed to us by the previous generations.

And what year were those fleet tests done sir ?