Thread still going on, eh.

The 5.56 NATO started out with a 14:1 twist & has ended up with 1:7 currently..
I have seen conflicting psi on the M855A1. Many say over 62k.
Heck, the M16/M4 has undergone over 150 changes over the years.


58k on the 6.8 SPC II seems to on the 'green/yellow line'.

The physical difference between the SAAMI & SPC II is small. But, it make a big difference in pressure. Especially, combined with proper land groove ratio/twist.
As seen in the 2008 6.8 testing.


PS I own page 5.

LOL

If you had the handbook, you would see your incorrect assumptions right away.  Western Powders has had solid engineering staff in the past.  I don't know what happened, but there is no way legal would sign off on one of them telling people the AR15 can take 90,000psi.  That's a major red flag right there, and also saying the AR15 doesn't have pressure containment issues.  The AR15's history of pressure containment started as soon as they chambered it in .222 Remington Special, aka 5.56x45.  It was even addressed in end-user Technical Manuals in the military with detailed inspection points for the soldier to look at when conducting Preventative Maintenance Checks and Services (PMCS), the bolt being the main problem child.

In our chapter on detecting abnormal pressure signs in Volume I of the 6.5 Grendel Reloading Handbook series, it's pretty clear that using the chronograph checked against published load data is the number one indicator for the common man.

Your terminology doesn't make any sense either, which is another testament to the level of experience we're talking about.

I think the part of the forum that would truly be a great fit for you is that way --------------->

It's called General Discussion.  You'll find a warm reception I think.

Edited...VA-gunnut

Trouble is you dont keep anything straight.
What was said was.
"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".
6.8 barrels are proofed at 70,000 but no catastrophic failure until much higher.

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.
You see I asked about catastrophic failure because you said you had seen it but could provide no proof.

I put it bold so that you just might read it this time.
Do you also see the part about being in that department for 7 years, same guy sir.
Same guy unless you co-authored the G manual more than 7 years ago.

I have NEVER stated that the 6.8 should be loaded over 60,000 psi ever.

The bolt is the limiting factor. However you have been screaming barrel tenon, hoop strength for what, four years now at least.
Now its the bolt, yea no kidding, its always been the bolt.
But see that wouldn't fit well with your game plan, because the bolts an even bigger limiting factor in the G now isn't it.

I am bringing technical data, technical information, from industry professionals.
To support what I have learned and discovered.
I have no bias, I am just not sitting back letting the misinformation flow.

Funny thing is this anti 6.8 campaign is what fueled me to go after real data and information as well as accelerate my learning curve.
So I guess thanks for that part sir.
 

You know, this could all be put to rest.  Push to get the spcII chamber SAAMI spec'd...

Has there ever been a "do-over" at SAAMI ?

The two factions defend their cartridge but I think the current trend will continue.
6.8 seems to have wider acceptance while Grendel will have its niche.

I agree with this completely.
As I have stated numerous times I have nothing against the Grendel, or any other caliber for that matter.

I think SAAMI would take a new submission. But perhaps someone else knows more about this.

What part of the case contains the chamber pressure?

Where does the gas pressure act?

Do you really understand how pressure works?

Gun Functioning  101:

The gas pressure act normal to every surface inside the case, so you break all theses pressure vectors into two components, one component acting purely radially and one vector acting purely axially.  The radial vectors we do not care abut at this time (they all cancel out in any case), but the axial vectors add up to bolt thrust.

As you can see this much exaggerated picture the for and aft forces act over an effective area that is basically the maximum internal diameter.  The internal geometry may vary from case to case, but the maximum internal diameter of the case will govern the bolt thrust.

Again, the ultimate answer: Wikipedia

Look , just pick a number. Really.

If we are ( thousands of us for over 8 years, including full auto shooters )exceeding this safe maximum by whatever means you measure it, then there would be a common problem of breaking bolts and other damage that you and others are saying occurs at and past that point.

Show me the broken bolts.

If then, you cannot , out of tens of thousands of bolts and hundreds of thousands of rounds, show me a failure trend due to surpassing that number, then we are not reaching it.

If we are not reaching it with the loads that we are using, then that number has no meaning in the end user's world, because the loads we are working up we have worked up to the point of showing pressure or seeing that pressure on pressure data systems and backing the loads down without issues.

Again, show me the broken bolts.

Academically, sure, I would like to see the exact number, correctly arrived at, but with the loads we are shooting, it is a moot point.

BTW, I am waiting on all of those pics of broken bolts due to this terribly over pressure, unsafe, and bolt thrust rating exceeding ammunition.

Here are the pressure limits:

Cartridge, 5.56mm, Ball, M193 - (MIL-DTL-9963) - 55,000 psi maximum average pressure, the maximum average plus three standard deviations is 61,000 psi

Cartridge, 5.56mm, Ball, M855 - (MIL-DTL-63989) - 58,700 psi maximum average pressure, the maximum average plus three standard deviations is 64,700 psi

Cartridge, 5.56mm, Ball, M855A1 - (MIL-DTL-32338) - 62,000 psi maximum average pressure, the maximum average plus three standard deviations is 66,000 psi

SAAMI specification for .223 Remington (SAAMI Z.299.4 1992 revised 01/11/2013) - 55,000 psi maximum average pressure (target), the maximum probable lot mean (max allowable lot average, MAP plus 2 SD) 56,400 psi, the maximum probable sample mean (4 SD above the MAP) 58,500 psi


The maximum suggested pressure for 6.5SPC IS NOT 58,000 psi!

From SAAMI Z.299.4 as revised in 2013 for 6.5 mm Remington SPC the recommended Maximum Average Pressure (MAP) is 55,000 psi.  This is the pressure that you should try to achieve with your loading.

The Maximum Probable Lot Mean Pressure is 56,400 psi, this is the maximum average pressure any lot should reach, this pressure is placed 2 standard deviations above the MAP. In any lot of ammunition, the 95.4% of the pressures developed should be below 57,800.

The Maximum Probable Sample Mean Pressure is 58,500 psi this is 3 standard deviations above the MPLM, 99.6% of the pressures developed in any lot of ammunition should be below this pressure.

When reading the SAAMI pressure recommendation, you don't just pick the highest pressure and assume that is a safe pressure to regularly load to.  If you shoot out a barrel with 15,000 rounds, the barrel bolt should only see the 58,500 psi pressure level 60 times.

So, basically what you are saying is, these numbers that engineers in the gun and ammunition industry come up with for maximum pressure and maximum bolt load can be ignored if nobody on a half dozen gun fora have pictures of broken bolts...

First, how many people actually load to these high pressure levels? People that use factory loading are using fairly conservative SAAMI pressure levels, even the SPC II loadings.  Second, where is there a database that holds all the broken bolt info out there?  There isn't one, so the only way you're going to hear about it is if they happen to post about it.  Guess what -  98% of the shooting world does not post on line (yet).

Personally, I have never seen a barrel that has been shot while full of cosmolene, and I cannot find any pictures on the internet specifically showing this condition, but guess what, I'm not doing it.

You're not real bright if you rely on negative information to make what can be safety decisions ("well, we have never seen a Pinto that has been rear-ended explode yet")...

The diameter that should be used is the overall diameter minus the wall thickness (both sides) just before the inside radius at the head. The most practical way to get that is to section a case and measure either the wall thickness or inside diameter.

Thrust on the bolt is multiplying the peak pressure in psi by the cross sectional area inside the case at its head.

BOLT THRUST

Bolt thrust is easy to calculate. Only two inputs are required. They are peak chamber pressure in PSI and as mentioned, the inside area of the case head that the gas pressure can work on. The formula then is:

THRUST=AREA*CPSI Where:

AREA=3.1416*(HS/2)^2

HS=the diameter of the inside of the case head.

Its the case head, period.

The proper place to measure a sectioned case is the point where the case head radius intersects the case wall.

Bolt Lug Strength

Which as Pav pointed out is much more of an issue with the PPC based cases.
As they have bolt head failure issues, where as the 6.8 does not.

Because after all the conjecture 7 years of running the 6.8 at 58,500 to 60,000 PSI has not produced ANY bolt failures.

Funny thing about the internet and forums.
If people are having problems, they go there to bitch.

By your way of thinking there must be one heck of a lot of broken 7.62x39/6.5G broken bolts!
If 98% of the people with them don't even post of the internet.

Funny how this has changed from its the chamber, its the chamber, it cant hold the pressure!
To now its the bolt, its the bolt!
No its the BS, no broken 6.8 bolts, on any gun forums, or any manufacturers forums.

If you cannot see how you calculate total thrust generated inside a pressure vessel, maybe you should not be giving advice on pressure loading things...

Especially when there is a picture that shows exactly how to do it.  What happens to the slight pressure that acts on the tapering walls of the case above the head?  Does that pressure just disappear?


Really, you know where every single 6.5 mm bolt is, when it was manufactured and how many rounds it had been shot, and know not one of them have failed.

Show me your data.

So, basically what you are saying is, these numbers that engineers in the gun and ammunition industry come up with for maximum pressure and maximum bolt load can be ignored if nobody on a half dozen gun fora have pictures of broken bolt...

I specifically mentioned that what you posted there was not the case. What I posted, is that if those numbers are correct, then we are not exceeding them, as there is no evidence of it, and yes, there would be a lot of pics of broken bolts. There are a lot less Grendels out there, yet, there is a ton of evidence that they were exceeding safe numbers regarding bolt thrust, with post after post after post of broken bolts, and the industry coming up with several solutions. That is not the case with the 6.8. And, there are thousands loading to spec II pressures in the 6.8, with no broken bolts.

I am not saying the numbers do not matter, but if you aren't breaking bolts with the common loads that are out there, even loads where you all are saying we're pushing it, then we are not reaching the pressures with those loads needed to generate the thrust necessary for it to be of consequence.

What I am saying, is if the bolt thrust number to not exceed is not being reached at the higher end of our hand loading, then it is not going to matter what that number actually is to the end user because he will not ever see that number so long as he stays within acceptable load data used by thousands upon thousands of hand loaders and factory tac / combat load shooters for over 8 years.

IOWs, like the old guy that holds up traffic. He never drives over 55mph, regardless of the road he's on. It makes no difference to him that the speed limit that cannot be exceeded is 65mph, because he is never going to drive that fast. He doesn't need to even see the sign on the side of the road.

We are not reaching the excessive bolt thrust number.

You say if we exceed that number over a certain period, then we will experience failures, bolt breakage, damage.

I agree, if we do that, we will experience failures, bolt breakage, and damage just as you say.

The reality is, we are seeing none of this, after 8 years. If we aren't seeing it, then .........

Do you realize your such a 6.5 fanatic that you typed it instead of 6.8 multiple times?
Funny how the brain works when we get worked up is it not?

Yet again.

No, it shows how little I care about either.  I prefer 5.56 or 7.62, no point it going in between...

All I know is 6.8 Remington SPC is not a 58,500 psi rated cartridge.  It is a 55,000 psi rated cartridge.

Grendel is a 52,000 psi rated cartridge.

The reason the pressure is lower for the Grendel is the case is larger in diameter (.307 sized), and has a larger bolt thrust.  The 6.8mm SPC is a slightly smaller case just a few thousandths below M43.

Actually the SAAMI chamber rating of 55,000 psi was due to pressure spikes from the .050 leade of the improperly submitted design.
This was further aggravated by the use of the .270 barrel specs.

It was not rated at 55,000 due to bolt or chamber strength. But due to a screwed up chamber drawing being submitted.

This is why in the SPCII chamber Western Powder has loads at 58,500, yet again.
The SPCII chamber with its longer leade is not subject to the pressure spikes, hence the ability to run a higher pressure.

Hows this:
BACKTHRUST
The force exerted on the breech block by the head of the cartridge case during propellant burning.

BOLT FACE
See Breech Face.

SAAMI

See that? SAAMI says the head of the cartridge case.

First hit in a Google search...

http://68forums.com/forums/archive/index.php/t-51656.html

3 in one thread, which has been archived in less than a year?

I don't know why they broke, and I frankly don't care...

You guys are exactly what you accuse others of being...

Awesome, you found a couple. I only see 2 in that thread and if you read it you can see how rare it is. The OP joked about getting it gold plated and engraved.
The other bolt from 09 with 6 to 8k rounds on it.
6.8 bolts are not magic, I had never seen one broken before. So it can happen, in any AR.
As I have always stated, show me something, then I will admit yes it can happen.
Which you did, so yes it can happen then, rare but can happen.

However this is not any proof that using the 6.8 at 58,500 psi leads to premature failure.

The biggest point of this thread has been chambers, show a broken or failed chamber.
And to that there are none.

That third bolt was one of the ones I mentioned in either this thread or another that was part of a batch withb improper heat treating. All of those bolts were replaced with in spec bolts, and the rest of the batch that didn't get out was sent back along with those as they came in.

A few people managed to not send them back for free replacement once the issue was caught.

Still, it took a long time.


The other bolts, we they broke, and as far as I know were proper bolts.

LWRC 6.8 Broken Bolt  

In addition to the shorn lug, you can also see a very pitted bolt face.



Not only is there a sheared bolt lug, but the bolt face is heavily pitted, with compromise of the firing pin hole.

For more education.  The bolt thrust diagram posted several entries above is an excellent reference because it shows the axial force is of course in both directions.  That slips past a lot of people.

The bolt is not your biggest worry, even though that's what shows up with a failure.

There is an inherent problem with the chamber when you exceed the rated spec for MAP regularly.  As the cartridge exerts axial load in both directions, what aspects of the pressure containment vessel are bearing the load?

The shoulder of the chamber is being pushed against by the case shoulder going forward
The bolt head
The rear of the bolt lugs
The face of the barrel extension teeth
The barrel extension shaft
The barrel extension threads
The barrel tenon threads

If you run an AR15 to the point that bolt lugs are shearing, what has happened to the barrel extension thread mate-up to the barrel tenon threads?  That's another place where you start to have problems.

And there still is an issue with potentially ringing a chamber over time in the unsupported relief cut area.  I've literally seen it happen, and it is a consideration for rifle actions when people try to stuff a fatter case into an action size that does not support the diameter and pressures.  .338 LM, .404 Jeffires, and other fat magnums in a Rem 700 long action have proven to exhibit setback or stretching, due to the bolt thrust and tenon thread limitations.  There simply isn't enough meat to hold the most high pressure containment systems of the firearm together.

Large Magnums in Rem 700 Discussion

All of the pressure containment considerations are valid.  Bolt thrust, hoop stress, metallurgy, bolt geometry, barrel extension diameter, barrel tenon and barrel extension thread mate-up all combine to provide a set of engineering challenges that need to be addressed by a competent design and engineering team, a competent production manager, and a competent vendor selection process.  These tasks are not easy at all to get right.

To date, we're just not seeing a sensible approach to the 6.8 when people are advocating for 58,500-60,000psi working pressures for a case with this geometry in the AR15.  A great effort has been made to bury and purge evidence of 6.8 failures, but it should come as no surprise that a bolt with less meat on it than a 5.56 bolt, run to pressures at or higher than most 5.56 loads will break a bolt, no matter what someone new to this claims based on their emotions in an environment absent of the facts.

Because there is no standardized set of specs for the cartridge, it makes understanding this that much more difficult for the manufacturer and hand-loader, especially as they are enticed by the claims from novices who are more brave than aware of the limitations of physics, and published data ranges from max loads of 53,600psi, to 58,500psi.

A rifle should have no problems running factory ammo in volume, as long as that ammo is kept in a sensible pressure range based on the above described limitations.  It should only encounter a handful of loads that push the upper end of Maximum Probable Sample Mean.  If it is run on a steady diet of higher pressure loads, bolt lugs will start to crack, tenon and extension threads will stretch, and you lose your torque between the extension and the barrel.  If you simply drop in a new bolt and keep firing, you're setting yourself up for something worse in the long run.  Extreme cold temps exacerbate this problem.  Most people don't know or care about temps, but I personally have to look at them.

For a military cartridge, passing off the extreme cold weather testing is the most difficult set of challenges for a new design. The 6.8 failed to even pass warm temperature fleet testing at Bragg, and instead of continuing the testing with recommended tweaks that could improve it, it was recognized that the program just didn't have competent advocacy.  You can relieve pressure by pushing the throat out, but that's a band-aid approach to a bad pressure rating in pursuit of increasing performance unrealistically. Therein lies the problem of the 6.8 SPC, SPC II, and a continuing devolution of anything resembling a standard, and for these reasons, I have stayed away from it, watching all this transpire from the start.

If you were to bring this in front of an equivalent venue akin to Shark Tank, there would be a lot of, "And for these reasons, I'm out."

That is the definition of bolt thrust/backthrust whatever you wish to call it.  Not how you calculate it.

Really, are you so... do you not know how gas under high pressure works?

Here is the picture again.  All of the little red horizontal lines that run into a surface on the right side of the case help push the case to the right.  the effective area of all those little red lines is the area labeled "effective area"



Here is a picture of a cartridge case:



The internal diameters at the red boxed distances are:

Internal dia @ .335"  = .3700"
Internal dia @ .710" = .3635"
Internal dia @ 1.100" = .3567"

You can calculate theses diameters with the .01746" TPI (taper per inch) and the distance from the known .3759" diameter and the listed minimum case thickness.  You can easily see that the case is shaped internally like the exaggerated picture above, it starts small grows to a maximum and then narrows down.  The pressure the pressure inside the case presses in all surfaces with a axial component.  This tends to stretch the case, if the case wall are friction-stuck to the walls of the chamber, but for a conservative approach best not count on that force being there, also, cases can separate.

If you want to used the actual head diameter (for a .223/5.56, this is .378) is an even more conservative approach.  But, if you think the force only acts on the .300" diameter because a picture on Wikipedia said so...

At the maximum average pressure (58,700 psi, for military M855 ammunition) the bolt thrust (minus case tension/friction) is about 6,500 psi, using the above listed maximum diameter.  For the proof load of 70,000 psi, the bolt thrust is 7,500 lbs or just about one Ford F350 hanging from the lugs.

From what information I have on the Remington SPC case internal dimensions, and granted it's not much, the maximum internal diameter is about .395" to .400".  For this dimension I get about 6,900 with a 55,000 psi SAAMI MAP, 7100 lbs for the MPLM pressure of 56,400 psi, and 7350 for the 58,500 psi load.

No matter how you pick the area you use to calculate the bolt thrust, if you do it the same way for both the 6.8 SPC and the 5.56mm, you will get that you are shooting 98% of a high pressure test cartridge with each 58,500 psi round.

It's your face that is snuggled up next to the rifle, take whatever risks you feel like, but going around saying loading SPC up to 58,500 psi is perfectly safe is tantamount to espousing that 5.56mm, M855, is safe to shoot in .223 Remington chambers....

You keep ignoring the fact that he isn't talking about SPC.  Completely different animal pressure wise from the newer chamberings.

ETA:  And to be clear, I don't know if he, you, or whoever else is correct.  Don't care.  I read this thread for some knowledge and especially the entertainment value.  But I do keep seeing people mention data relating to SPC, and a lot of that is irrelevant now.

Thank you

They keep also ignoring the fact that Western Powder ie the professionals, not armchair quarterbacks.
States that there is no problem with the bolt or chamber running to 6.8SPCII loads to 58,500 in their published reloading manual.

The G fans will always fall back to the SAAMI chamber.

so...............

58000psi is some how different than 58000psi?

The spc might have generated that much pressure sooner with less velocity, but we are talking about generating 58000psi in the spcII case as well....

Unless I missed something.

Yeah I guess.  Same as 5.56 and .223 chamber right?  One's perfectly fine and might be "hot" in the other I suppose.

FWIW:  I've never loaded for either.  So I haven't done any firsthand testing.  But I do have a reloading manual sitting beside my computer that has the same kind of numbers in it that Yama mentioned in his OP.  But once again that is in an SPC chamber.  I don't know if those loads are actually getting those high of pressures in the SPCII.

They also state that the loads are interchangeable between SPC and SPCII as well.....

It states:
"These loads apply to both 6.8SPC and SPC II."
Not that they are interchangeable.

If you work up a load in a SAAMI chamber you will hit pressure signs at 53,000 to 54,000.
If you work the same load in a SPCII chamber they do not appear until the area of 58,500 to 60,000
I am referring to the same brand powder, primer, projo, case, OAL etc.

Let me clarify this.

You will hit pressure signs at the same pressure in either chamber, which is around 58k-60k.


You will reach that 58k-60k in a SAAMI chamber 150-200fps faster, and at a lower powder charge than you will with a Spec II chamber.

In other words, a max load listed in a book that shows 26gr of X powder reaching 2500fps @ 58K in a SAAMI chamber will be at a much lower pressure but the same velocity in a Spec II chamber.

The load for the Spec II chamber would be between 2-4gr more. It would look more like 29gr of that same x powder reaching 2700fps @58K.

So what you have, is the data in the books are worked up and tested in the SAAMI barrels, as stated by the powder companies , since SAAMI is approved for them to work from.

The SAAMI load will max out in the SAAMI chamber well before it will max out in the Spec II chamber.

Thus, the SAAMI load is for both SAAMI and Spec II guns.


If these loads were worked up and tested in a Spec II chamber, they would be dangerous in a SAAMI chamber, and,  just like the Tactical and Combat factory loads, would be listed as for Spec II only.

It really isn't that hard.

A hot load in a SAAMI chamber is a barely workable load in a Spec II chamber.

A normal load with safe pressures in a Spec II chamber is a very hot, over pressure and dangerous load in the SAAMI chamber.

Hence, loads worked up in load data books using SAAMI chambers are safe in both.

Let me add further, if you look at the PDF of the testing with pressure systems you will see exactly what I am saying.

Now, my challenge to any who doubt.

Buy an old SAAMI barrel , build an upper or buy an old SAAMI upper that has not been reamed to Spec II, and bring it with you.

We'll use my hand loads.

I'll shoot my gun, and you shoot yours, and we can film it and take pics.

I'll even buy you a couple of hot dogs, hell, make it steak, it may be your last meal.

One thing about this "There ain't no broken bolts" argument...

Negative data (things NOT happening) is a dumb way to look at safety.  Let's look at this same argument in a different industry:

The question:  "I have noticed that you are recommending flying the Boeing 737 outside of Boeing's published recommendations.  It that safe?"

Your answer: "No one has crashed."

That is not an argument, that is a joke.

And, that is exactly the same as what you are saying.  Some of us are asking you "Why do you think 58,500 PSI in  6.8mm SPC is safe?"

And your answer, "Because nobody has broken a bolt (except those two, and any others not posted up on the web), yet."

Sorry, but that argument is stupid, period.

Whats really stupid is all the argument against data that is set by an established company that is one of the leaders in the reloading industry.
As well its one that is quoted by LR is his G loading guide.
Which would then make everything in that guide questionable.

Here you go, I got permission to share the latest data.


Safe at 58,500 bolt and chamber.
Don't that just beat all......

And Accurate lists 58K as the max on most of their loads as well, including the AA2200 110gr load, which ha been my go to load of late.

Again, in the data above in Yama's post, the barrel used for testing is a SAAMI chambered 1/10 twist which will produce that 58K about 150-200fps lower than the Spec II 1/11 barrels will as shown in pressure tests.

Curious, will shooting loads at the 58k PSI regularly accelerate wear though, assuming it is 100% safe?

All we know from Western's published reloading is that their load generates 58,449.

Yes, I suppose the implication is that Western's engineer believes it to be safe in AR15-type weapons and believes it does not expose them to liability claims. You make a fair point.

But is he right or is he wrong? Upon what basis does he believe that? A wave of the hand and, "Big whoopie"? We still don't know how he decided upon that figure. Why not 59,000? Why not 57,500?

If he knows something about the AR15 weapon series that the rest of us could learn from, I'd be interested in hearing how he responds to your questions when you visit, how he squares his assumptions with the U.S. military safety limits for 5.56 — mentioned above — extrapolated to an even bigger cartridge.

Of course it would.
If you run max safe loads in any weapon vs moderate loads it will cause more wear.

My hunting loads arerun at the top accuracy node, its not about a "drag race" as LR likes to put it.
My long distance loads I run at the top accuracy node.
Target loads at the lower accuracy node.

You guys want to talk about running the weapons for military usage? So cool, I am glad your finally admitting the 6.8 should be seen in that light.
It is the best GPC available after all :)

I would like to see how each powder company comes up with that limit as well, but , you have to understand that the data would not be published were it not safe data for the gun it's intended for and the shooter. In fact, most max loads today are conservative to a point, some more than others, but it is to allow for a range of users to load to if no signs are present , and not damage their firearms or themselves and open the companies up to lawsuits.

So my point earlier, was , that all of these companies say that x amount of chamber pressure us safe with a powder and B bullet, and that this testing was done in a SAAMI chamber.

We also know that according to tests by ammo companies that load spec II tactical loads, and 6.8 manufacturers, have also tested ( with testing equipment ) the load data that we load to with the spec II, and find that the same threshold of chamber pressure is reached with a larger powder load, and in general, 150-200fps more in velocity.

So basically, for instance.

SAAMI- 2550fps 110gr load with X powder produces 58K.
Spec II -2700fps 110gr load with X powder produces 58k.

If the limit is indeed 58K, then that is reached with more powder in the spec II at higher velocities. The gun doesn't know anything but the pressure exerted. It doesn't matter if it's from 27grs of x powder or 30.0grs, it doesn't suddenly become dangerous and prone to breakage just because the bullet is going faster.

Simply put, Spec II allows for faster velocities with the same projectile with the same pressure as the SAAMI chamber does for the slower projectile.

When SAAMI changes the 55000-58000 the above would have a lot more meaning....

Again, a fair point, and I generally agree. However, it IS a total assumption on our parts. And there are inconsistencies, as some here are trying to point out, that make one wonder.

I've been around long enough — and seen enough of the inside of the gun industry — that you'd be surprised how mom-and-pop and fly-by-the-seat-of-your-pants a lot of it actually is. People just pick up something they assumed someone else tested and just run with it. I will grant that the fact that a company is willing to expose themselves to the liability of selling something is a valid data point, but it is certainly not definitive.

By the way, you've been trying hard to educate us on the differences between the 6.8 and 6.8 II. Thanks, but I think we get it. And that's not the issue we're discussing here.

If you were to ask, oh, SSA (the originators of "combat" loads — which I don't know if they still sell) or, oh, Bill Wilson (popularizer of high-velocity SPC II loads — until they, interestingly, discontinued those) how they decided upon 58,500, what would they say? "Uh, we tested it and didn't see any swipes." Or . . . "We ain't blown a gun yet, so it's all good."

I think you'll find the current state of the argument is circular: "Well, we did it cuz THEY did it, and didn't seem to have any problems." "Wait, a minute, I did it cuz YOU did it."

So I'm wondering if Western has something more definitive to report.

SSA is now Nosler.
Wilson stated in the 68forums they stopped the tactical loads for now due to having powder supply problems.

I find it very interesting you G guys are arguing with the 58,500 for the 6.8 but your totally ok with the 52,000 for the G.
Which is well above the 50,000 from the weapons designer.
While saying oh well, he was conservative.

Heres another quick one for you.
SAAMI certified the 6.8 with Rem large primer brass, which does not hold pressure as well as small primer brass due to the case size.
This is why everyone except Rem has went to small primer.

While a small primer would make a difference in brass, it does not change the firearm.  Many cartridges have been handy capped by the firearm design.

ps @ this point the only one bringing other cartridges into this conversation has been you.

Team 6.8 up by 12
4th quarter, 1:30 min left
Team G can't buy a bucket

Ha! Good one, DD. Gotta at least have a sense of humor about the whole thing, huh?

Thanks for the info!
Boy, that M855 has a high psi! WOW!

I see 'bolt thrust' mentioned multiple times here. ....Strange?..... No mention of freebore or leade/throat...Does frreebore have nothing to do with pressure? I mean, we are talking about .05 vs .100 freebore. Then there is land;groove ratio, poly vs Enfield vs 54R treatment/lining etc. A common SPC II COAL is 2.295. you can't do that with SAAMI specs.

FWIW- The 55k limit had to do with both pressure spike & military requested 55k to keep control of the weapon at full auto for the initial test around '04'.

Why is a 260 Remington rated at 60000 psi and a 6.5x47 with small primers rated at 63900?
Same dia case in the same Remington rifle. The Lapua case can handle higher pressure.
What ratio of cartridge trust to bolt strength do they consider strong enough. Should the bolt be twice as strong, 2.5, 3 times as strong what?