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7.62 X 51 cartridge vs. .308 Winchester: the differences!

This is a discussion on 7.62 X 51 cartridge vs. .308 Winchester: the differences! within the Ammunition forums, part of the M14 M1A Forum category; Huh?...


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Old December 7th, 2012, 10:12 PM   #61
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Old December 7th, 2012, 10:33 PM   #62
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Hey, RAMMAC...

No need to bring my name up in the above post...

I'm a big boy and I've been around this forum for a bit. If somebody new posts something I agree with, I'll say so. NOTE: I only commented on his references to SAAMI and CIP pressures. You kinda tossed me into the other pot for no good reason. He accurately referenced the documents which are available to everybody here.

Newbies have good info also.

In fact, one of the problems here from time to time is the unquestioning belief in some of the "old hats" who sometimes also don't have things right.

Let's look at this pressure thing from a pragmatic viewpoint:

If the 30-06 has a max pressure somewhere around 62,000 PSI and is fired in the GARAND...(That cannot be denied...the 30-06 has been around for a long time...) , then doesn't it follow that the 7.62mm NATO, which replicates the 30-06 ballistics (muzzle velocity) also has the same pressure (fired from a Garand sibling...)?? The M14 gas system is Superior to that of the Garand, so should handle pressures even better.

IF the 7.62mm NATO has a 52,000 PSI pressure then it follows that the muzzle velocity must be considerably lower. Why would the US Gov't load a modernized cartridge 20 percent lower than the 30-06? (which they did not...)

The Polish document you quoted above is simply incorrect. They fell for the same ambiguity you did. Heck, you may as well quote Wikipedia http://en.wikipedia.org/wiki/7.62%C3%9751mm_NATO

"Maximum pressure 415 MPa (60,200 psi)"

But that's OK, we can agree to disagree. Just be aware that other folks here who are just as intelligent as you can arrive at different conclusions.

No need to belittle my comments.

Okeee-Dokeee?

JWB

PS... BTW... the SAAMI documents, if you decide to read them, say that C.U.P is acceptable for pressure testing, but must not be confused with transducer methods... They even have the drawings for the setup for the crusher method, even today (not waay back in the '60s).


Last edited by jbrooks; December 7th, 2012 at 10:44 PM.
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Old December 7th, 2012, 10:37 PM   #63
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Quote:
Originally Posted by bigedp51 View Post
The thread topic is "7.62 X 51 cartridge vs. .308 Winchester: the differences!"
And the European CIP considers both of them to be the same cartridge.
And the "quick load" figures are NOT compensating for the throat variations between rifles.
Sorry, but you're wrong again.

In QuickLoad you can modify the cartridge dimensions to reflect any condition. If you want to be very specific, the software allows you to change the shoulder position and the bullet seating depth to reflect the conditions that would be match the moment that the bullet reaches the lands. Normally that's unnecessary and going way overboard considering that the normal amount of deviation in pressure that a rifle will experience due to environmental conditions. The default is for the software to use the SAAMI or CIP standards as a basis for calculations, some cartridges were loaded in to the database with SAAMI specs and others with CIP specs.

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Old December 7th, 2012, 10:58 PM   #64
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Sorry, I didn't read the entire post till later...

Quote:
Originally Posted by RAMMAC View Post
...Oh and on a final note; jbrooks, ...You're like the playground bully that cries to the teacher when the guy he is picking on kicks his behind.

??? I'm missing something here...

If anybody is doing the peeing it's bigedp51, he's the person that is acting like I'm some fool that has no idea what I'm talking about and you aren't much better with your implication that I didn't understand about the CPU vs. PSI issue,

RAMMAC, I've read most of your posts over the years. I never implied you didn't know the difference. I'm saying you're wrong about the pressure "differences" between the .308 and the 7.62 NATO. It's that simple.

you should know better, you've been around long enough to know that I've had this discussion many times over.

Yes, you have. Doesn't mean I can't comment on it.
Really, RAMMAC, talking down to me as if I were a child doesn't do much for the dialog. You should know better...

JWB

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Old December 7th, 2012, 11:17 PM   #65
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One more thing...

All this referencing of QuickLoad is, frankly, a real load....

I actually have access to a lot of research material from US Army,including several papers and a couple books on interior ballistics.

You may want to check AMCP-706-106, "Engineering Design Handbook, Part 1". A good elementary tutorial on the chemical reaction of powder in a gun chamber and the pressure equations, etc.

I can tell you that Quickload is a simple simulation, made for the mass market.

Garbage in, Garbage out. I like QL myself, but I don't comsider it to be an authority on the true behavior of the cartridge.

You may want to delve into the processes used to calibrate QuickLoad...

Like all simulations, it makes pretty curves, and the more colors the prettier. And the prettier, the "more better" the data must be.

If Quickload were so great, then SAAMI, the US Gov't and CIP would do no more actual testing.

But we all know better...

JWB


Last edited by jbrooks; December 7th, 2012 at 11:29 PM.
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Old December 8th, 2012, 01:36 AM   #66
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Quote:
Originally Posted by jbrooks View Post
Hey, RAMMAC...

No need to bring my name up in the above post...

I'm a big boy and I've been around this forum for a bit. If somebody new posts something I agree with, I'll say so.

Newbies have good info also.

In fact, one of the problems here from time to time is the unquestioning belief in some of the "old hats" who sometimes also don't have things right.

Let's look at this pressure thing from a pragmatic viewpoint:

If the 30-06 has a max pressure somewhere around 62,000 PSI and is fired in the GARAND...(That cannot be denied...the 30-06 has been around for a long time...) , then doesn't it follow that the 7.62mm NATO, which replicates the 30-06 ballistics (muzzle velocity) also has the same pressure (fired from a Garand sibling...)??

IF the 7.62mm NATO has a 52,000 PSI pressure then it follows that the muzzle velocity must be considerably lower. Why would the US Gov't load a modernized cartridge 20 percent lower than the 30-06? (which they did not...)

The Polish document you quoted above is simply incorrect. They fell for the same ambiguity you did. Heck, you may as well quote Wikipedia http://en.wikipedia.org/wiki/7.62%C3%9751mm_NATO

"Maximum pressure 415 MPa (60,200 psi)"

But that's OK, we can agree to disagree. Just be aware that other folks here who are just as intelligent as you can arrive at different conclusions.

No need to belittle my comments.

That makes life interesting...

JWB
If you didn't want to be brought in to the conversation then why did you enter in to it, for that matter your last post is just adding more fuel to the fire, you certainly don't seem to be acting like a guy that doesn't want to be in the conversation. Big boys are prepared to deal with the consequences of their words and deeds.

As for your first assumption above, no it does not follow that the 7.62mm NATO would produce the same pressures in order to achieve the same velocity as the 30-06. I assume that you are basing your theory on the two rifles producing the same velocity with the same weight bullet. The first problem with that assumption is that you aren't taking in to account the barrel length difference, the Garand has 2 inches more of barrel length and that allows the bullets to attain higher speeds than the M1A's 22" barrel. That means they had to come up with a way to compensate for the shorter barrel, they had to get the bullet up to the same muzzle velocity quicker. The only way that they could do that was to use a smaller case that would cause the pressure to reach a higher maximum and in turn would cause the bullet to gain speed quicker. Since the .308 case has less volume, it will always produce higher maximum pressures than a 30-06 case (given the same bullet weight) and since the Garand has a longer barrel it will always produce higher velocities than the M1A, all other things being equal. Where you make your mistake is you are making the assumption that if the muzzle velocity is the same then the pressure behind the weight bullet must also be the same. You are right, but only in regards to the pressure at the muzzle.

According to Hornady's 9th edition loading manual, if we load a 168gr Hornady Amax over 43.9 grains of IMR 4064 and seat the bullet to get a cartridge overall length (COAL) of 3.220" we should produce the following (along with a case volume of 68gr of H2O);

Max Pressure - 40886 psi
Muzzle Velocity - 2496 fps
Percentage of usable case volume used by powder charge - 86.6%

The Hornady manual says that you need 41.6gr of IMR 4064 to push the 168gr Hornady to 2500 fps in the M1A, I had to use 41.1gr in my QuickLoad software to get a close match between the 30-06 velocity and the .308 but they ended up within 1 fps of each other.

Max Pressure - 47103 psi
Muzzle Velocity - 2495 fps
Percentage of usable case volume used by powder charge - 97.7%

So in order to get the same velocity as the 30-06, using the same powder and bullet, you need 2.8gr less powder in the .308 as opposed to the 30-06. At the same time, the max pressure would be 6217 psi higher in the .308 than the 30-06. If you look at a pressure/velocity/time curve you would see that the .308 pushes the bullet up to speed faster than the 30-06 does and that makes sense because the shorter barreled .308 needs to get the bullet up to speed sooner than the longer barreled 30-06. That's why they picked the .308 cartridge for the M14, it has the volume that they needed to create the higher pressures that they wanted in order to push the bullet to the same muzzle velocity.

So your assumption that max pressure has to be the same since both rifles have the same pressure at the muzzle is wrong. The M1A produces higher pressures that move the bullet to speed quicker than the longer barreled Garand.

As for your claim that the Polish document is incorrect, in what way? What ambiguity? You simply say that their information is incorrect without any proof or facts and you say that I'm being ambiguous? I provided a document that is a copy of a government report in regards to the acceptability of NATO ammunition and you provide nothing to substantiate your claim that the report is wrong and you call me ambiguous...amazing, talk about hypocrisy. Just saying that it's incorrect doesn't prove anything, you can't get away with just saying that my proof source isn't valid, you have to prove it's not valid, otherwise your argument has no credibility what so ever. I can make the same claim; all of your information is incorrect so I reject any and all arguments that you make. How are we to get anywhere if we both arbitrarily reject information because we feel like it. If you want make the argument then you have to be willing to supply facts to prove your assertions. I supply facts to back up my statements, you haven't.

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Old December 8th, 2012, 02:17 AM   #67
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Quote:
Originally Posted by jbrooks View Post
One more thing...

All this referencing of QuickLoad is, frankly, a real load....

I actually have access to a lot of research material from US Army,including several papers and a couple books on interior ballistics.

You may want to check AMCP-706-106, "Engineering Design Handbook, Part 1". A good elementary tutorial on the chemical reaction of powder in a gun chamber and the pressure equations, etc.

I can tell you that Quickload is a simple simulation, made for the mass market.

Garbage in, Garbage out. I like QL myself, but I don't comsider it to be an authority on the true behavior of the cartridge.

You may want to delve into the processes used to calibrate QuickLoad...

Like all simulations, it makes pretty curves, and the more colors the prettier. And the prettier, the "more better" the data must be.

If Quickload were so great, then SAAMI, the US Gov't and CIP would do no more actual testing.

But we all know better...

JWB
Man, it's obvious that you have an axe to grind. Look, you can reference all the books you want but ridiculing belittling something without evidence and trying to attack the person rather than the idea is proof that you really have no argument.

While you may have access to resources it's clear that you don't understand them as well as you think you do. Just the claim that the pressure in a .308 and 30-06 has to be the same because they have the same muzzle velocity proves that you really don't understand pressures and velocities. You are really amazingly myopic, you accuse me of being disrespectful and yet you don't see it when you do the same to me.

QuickLoad is far from a simple simulation, it is valid enough to be used by Berger Bullets to build their reloading manual and I know that several bullet companies use it to make estimates while developing loads. Just because you don't agree with the tool doesn't mean that it is garbage. Garbage in/ Garbage out is a phrase that means that if the person that inputs the data enters inaccurate information then he will get bad information out, are you saying that I am putting garbage in to the software? If so then explain why my numbers match just about any load that you find in any of the reloading manuals? Prove your point, provide me with a load from a reloading manual and I'll provide you with a desktop snapshot showing the resulting information from QuickLoad. It's software and you have to be smart enough to know how to use and to also understand it's limitations. I'd never assume that it is infallible but I know that it's accurate enough to help me build loads safely and help guide me to an optimum load quicker than without it.

As for your recommendation that I dig in to AMCP-706-106, "Engineering Design Handbook, Part 1", do me a favor and grace us all with your knowledge, post some information form the book, like maybe an equation and then explain what it means and show us how to solve it. Explain the parameters that the equation represents. If you want me to check the book out then provide me with a way to get my hands on it. I'm more than willing to take up a challenge, are you? I'm not afraid to say that I don't understand something, are you? I have no problem with your attempts to insult me but either start proving some of your claims or drop it.

I know what QuickLoad says that they did to calibrate their software but since it seems you have some secret information please explain it all of us. I'm more than happy to be taught something new, are you willing to teach me? If you want to impress me then start proving how much you know.

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Old December 8th, 2012, 04:27 AM   #68
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Quote:
Originally Posted byRAMMAC
While the technical specifications for both the .308 & 7.62 cartridges and rifle chambers are different to varying degrees, in reality there is virtually no difference between the cartridge dimensions and minimal difference between the chambers.
The throat is part of the chamber and the M14 has a longer throat than the .308 so your above statement is wrong.

What is wrong, explain your comment. Are you saying that there is no difference between the chambers? It looks to me like I was saying that there are differences but they aren't large differences. How is that wrong?

Does the M40 have the same chamber and headspace as the M14, the answer is no. Do all 7.62 NATO rifles regardless of the country they are made in have the same chamber and headspace dimensions, the answer is no.

No? No what? No two 7.62 or .308 rifles have the same chamber and head space dimensions? Really? I guess SAAMI and CIP exist just for laughs and giggles. If no two rifles have the same dimensions than why does SAAMI and CIP exist, their very purpose is to standardize the specifications for the cartridges and chambers. This is just goofy rambling that doesn't make any sense to me.

Quote:
Quote:
Originally Posted byRAMMAC
The proof of that is that the TM lists M16 cartridge pressures as being about 50,000 - 55,000 PSI depending on which cartridge you are talking about.
Again you are wrong, the M193 52,000 reading is in cup and the M855 55,000 reading is the transducer method.

Again, how am I wrong? The values in the TM vary from 50,000 to 55,000 PSI, depending on which cartridge you are talking about. You claim that the M193 value is a CUP value, so that means that their claim of 52,000 PSI is actually 52,000 CUP. As you say that is equivelent to about 55,000 PSI, that would mean that the pressure value for the M193 is in the range of 50,000 - 55,000 PSI, as I said...so where am I wrong? I don't agree that their value is in CUP but while I can't prove that, neither can you...or if you can then post the proof. What's more, if my statement is wrong then there are a lot of countries that have the same wrong information since I was able to find two European sources and they indicate that these are NATO and CIP pressure values. How is it possible that an American pressure specification, improperly identified as PSI when in fact the number is in CUP units, would somehow match a PSI value that was derived from a European kPa value. I submit that the odds are pretty slim that those numbers would match unless they were based on standardized PSI values.

Both are the same exact pressure using two different methods of measuring this pressure, copper units pressure and the piezo electric transducer.

Prove it, scientifically there is no way that you can prove any CUP value is the same as a pressure derived from a transducer. Show me mathematical proof that CUP to PSI conversions are accurate across a range of normal rifle chamber pressures. CUP values are estimates based on the compression of a copper cup. Since the CUP process is based on estimates of pressure converting their values to PSI would still only be an estimate and not as accurate as the measured PSI values provided through a transducer. Transducer measurement devices are calibrated and produce directly measured pressure values. What's more, there is no accurate way to calculate equivalent pressure PSI values from CUP values.


Quote:
Originally Posted byRAMMAC
The average chamber pressure for fifteen 20-round series cartridges...shall not exceed 365 MPa...
365 MegaPascals is about 53,000 PSI.
Then "WHY" does the Army TM list 55,000 psi for the M855 M16 round, and 52,000 psi for the M193 round. Your mixing apples and oranges, your answer is wrong and a little fruity.

Well let me first point out that if you continue to be a smart A$$ we can end the conversation really quickly, if you want to accuse me of being fruity then you are getting personal and I really resent it.

Why does the Army list a higher pressure for a cartridge that uses more powder and a heavier bullet (the M855)? It's pretty obvious isn't it? I'm not mixing anything, I simply pointed out that the NATO pressure values match the values that the Army listed in their TM. Since the one corroborates the other then they must both be pretty accurate. I don't see how that can be confusing.


52,000 cup (copper crusher)
55,000 psi (transducer method)
62,000 psi (European CIP transducer method)

The above three pressures readings are one in the exact same pressure and are just measured using three different methods.

OK, so what? What's your point? All I see here is that you proved different measuring methods provide different readings, gee, there's a news flash. Oh, and by the way, if you are implying that the European PSI value is their max pressure value then once again you are proving how little you really understand. The 62,000 value is the equivalent of our proof load value, the Europeans specify this value as being 125% of the case's max pressure, it isn't the max pressure that is to be used on a daily basis.

Quote:
Originally Posted byRAMMAC
Also you are a little behind the times with your comment about the CUP vs PSI problem in the Army's TM, I pointed that issue out more than two years ago on this very forum;
Again you are wrong about me being "a little behind the times" this is my first posting here and its impossible for me to be "a little behind the times" when my joke tire pressure gauge photo is over ten years old. So therefore your post count and when you posted your information means even less to me because your information is still wrong.

Wow, you can't even understand normal conversation can you. How does the fact that you are new to the forum have any bearing on the reality that you are not up to speed on what I do or don't know. Being "behind the times" means that your aren't informed about what is currently going on, the fact that you are new here is exactly why your ARE behind the times. And since I am saying your behind the times in relation to what I know or don't know, you can't tell me that you are not behind the times, I am only person that could determine if you are since the concept is based on what I know. But that would be true of anybody that had just joined the forum. Why are you trying so hard to be an insulting jerk. This was just a phrase that accurately described your knowledge about the things I know and have discussed. Take a pill and relax. I was referring to the fact that you had no idea that I've been talking about the inaccuracy of the TM manual's pressure numbers for years. I put up with a lot of arguments over that issue and to now have somebody come along and try to lecture me about the same thing is really irritating and insulting. If you had started out by being reasonably civilized and said something to the effect of “RAMMAC, are you aware that there is a problem with the pressure numbers in the TM?” I would have said, “Oh yes, I am, but thanks for pointing that out.” Instead, as a guy with 1 post to your credit, you acted like you were some kind of gift from on high and were going to tell everybody how stupid they are.

The biggest problem with all this chamber and pressure guessing is that you are all forgetting the longer military throat when the pressures are actually measured vs SAAMI pressures with its shorter throat. And the military doesn't use QuickLoad to guess at the chamber pressure readings, they use actual test pressure readings.

Wow, do they really? I would have never known that the military used instruments to test pressure, man now I'm learning some good stuff. The funny part is that while they don't use QuickLoad to determine pressures, QuickLoad does in fact produce matching information so while it might not be your favorite tool, it does seem to be accurate, if you are smart enough to know how to use it.

Could you explain what you mean when you say
“The biggest problem with all this chamber and pressure guessing is that you are all forgetting the longer military throat when the pressures are actually measured vs SAAMI pressures with its shorter throat.”

It's difficult to understand what you mean since your sentence structure is so poor. Are you saying that we are forgetting that the military pressures are lower than the civilian pressures? I thought that Europe considered the cartridges the same. I also thought that you explained that all these pressures are the same regardless of measurement unit; CUP, U.S. PSI, or European PSI values.


And my Savage .223 bolt action has a longer throat than my AR15 HBAR with a 5.56 military chamber. This is because commercial rifles must have chambers and throats long enough to fit the company lawyer inside the chamber and not cause any law suits.

Have a nice day, I have to go now and put 220 kPa in my car tires.

Another childish insult, I guess it's the best you can do isn't it. And here I thought you might show some maturity, how wrong I was..

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Old December 8th, 2012, 05:36 AM   #69
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This is a very long standing discussion. My primary reason for following it is issues with my Springfield M1A - 95 production with TRW bbl. It cycles & runs great with american ammo, civilan and even military LC 308. When I run Radway green (from several eras) thru it, it loads fine, fires fine, then seizes in the chamber & won't extract. Have ripped out several extractors on the stuff, yet it runs fine in my Remington 700 LTR. One would think that my TRW bbl would be fine with mil spec, but.....ya, I know, send it back to Springfield to have it looked at, however I REALLY don't want to run the risk of loosing my TRW bbl. Perhaps have the chamber reamed / lengthened a touch ( I know, mess up the crome lining a bit ).

Everyones thoughts please....

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Old December 8th, 2012, 09:00 AM   #70
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Quote:
Originally Posted by bigedp51 View Post
Your problem is you are shooting British Radway green 7.62 ammunition in a American made M14 rifle. Your ripping out extractors because the cartridge case is still gripping the chamber walls when the bolt is cycling (over gassed)
Sounds reasonable on the difference in pressures but, if this is the cause, there's still the question of why is the brass still stuck in the chamber & has to be driven out with a rod later as opposed to being easily removed after the chamber pressure drops. Sorry if I didn't clarify this part of the problem in my OP. If it was just a momentary / pressure related situation, then the brass should be easily removed minutes later.

I know, save the Radway Green for my next FN & get over using it in the M1A...even though I have 3 ammo cans of it...
And thanks on the link to the adjustible plug, didn't know they existed!

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Old December 8th, 2012, 11:00 AM   #71
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Quote:
Originally Posted by bigedp51 View Post
Question: When you drive the Radway green case from the chamber does the rear of the case have the imprint of the ejector hole on the base of the case. Meaning does the brass show indications of flowing into the ejector hole of the bolt face, this is an indication of high pressure.

High pressure signs below.

I'll check next time I get to the field, thanks !

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Old December 12th, 2012, 02:27 PM   #72
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Quote:
Your problem is you are shooting British Radway green 7.62 ammunition in a American made M14 rifle. Your ripping out extractors because the cartridge case is still gripping the chamber walls when the bolt is cycling (over gassed)
I totally agree with this.

The pressure curve on your Radway Green is inappropriate for your rifle. Why?, I don’t know, don’t have a pressure gage to test. It could be that your surplus ammunition is old and it is higher pressure now than what it used to be. Could be as Ed says, not made for your rifle.


Quote:
Slamfires are not common, most often they are caused by a weapon that is out of spec due to wear or manufacturing defects. Incorrectly assembled hand loaded ammunition or hand loaded ammunition that uses inappropriate components is another cause of slamfires. If you have a rifle that meets the minimum safety standards and your ammunition comes from reputable sources you shouldn't have any slamfires.
While it is true slamfires are not common, if you shoot enough rounds, or are around people who do shoot enough rounds, you will have them or see one or be told of them by people who witnessed them. It is only an academic issue to those who sit behind their computers on Saturday, not to those who are shooting their rifles in weekend matches.

It is amazing how people forget the contribution primers make to slamfires. These mechanisms have free floating firing pins. The so called “safety bridge” is nothing of the kind and is an inadequate and certainly not positive means of preventing the firing pin from hitting the primer before or during cam down. If your round is a little fat, little long, if the bird of paradise flew up your chamber, the bolt will stop to crunch fit the case and that firing pin is free to wack the primer and what happens after that all depends on primer sensitivity.

You want to use the least sensitive primer in these mechanisms not the most sensitive primer. Sometimes the least sensitive primers slamfire, but the majority of slamfires, in battery or out of battery are with Federal primers, the most sensitive primer on the market.

I recommend CCI #34 primers, they are advertized as mil spec, the next type are TULA7.62, they are described as mil spec, and failing the availability of those, use CCI standard.

If you use Federals and have a slamfire don’t mention on this forum. The same person who recommends federals will chase you around, discrediting you for admitting that you had a slamfire:


Last edited by XXIV Corps; December 12th, 2012 at 03:25 PM. Reason: ROE #5, stay on-topic discussion which is missing here...
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Old December 12th, 2012, 09:08 PM   #73
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Quote:
Originally Posted by RAMMAC View Post
...As for your recommendation that I dig in to AMCP-706-106, "Engineering Design Handbook, Part 1", do me a favor and grace us all with your knowledge, post some information form the book, like maybe an equation and then explain what it means and show us how to solve it. Explain the parameters that the equation represents. If you want me to check the book out then provide me with a way to get my hands on it. I'm more than willing to take up a challenge, are you? I'm not afraid to say that I don't understand something, are you? I have no problem with your attempts to insult me but either start proving some of your claims or drop it.
I know what QuickLoad says that they did to calibrate their software but since it seems you have some secret information please explain it all of us. I'm more than happy to be taught something new, are you willing to teach me? If you want to impress me then start proving how much you know.

I know what QuickLoad says that they did to calibrate their software but since it seems you have some secret information please explain it all of us. I'm more than happy to be taught something new, are you willing to teach me? If you want to impress me then start proving how much you know.
Hey, rAMMAC…

At one time you said this about me: (Post 127, at Regarding that "Safety Bridge"...)

Quote:
Originally Posted by RAMMAC View Post
Kudos jbrooks, not only am I impressed with your integrity but also the information you posted and how you validated the facts about the function of the bridge. Your comments are very well supported with measurements and pictures. I think that your posts are very informative to those of us who don't approach the topic with preconceived notions and ridiculous conspiracy theories.
So I Consider you to be a man with whom I can reason and exchange ideas. I’m not trying to be an ass, nor am I trying to be an “alpha male’ as one of our more recent members rather clumsily tried to insinuate.

I am a big boy, and I appreciate efforts to keep this dialog on a mature level.

As to the reference, the full title is

Engineering Design Handbook - Elements of Armament Engineering, Part One - Sources of Energy: (AMCP 706-106)

And you can get it off the web from many sources.
Chapter 2 , “THE THERMOCHEMISTRY OF CHEMICAL EXPLOSIVES” contains a subchapter “PRESSURE A GUN PROPELLANT CHAMBER” and there you will find all the basic equations needed, along with examples using smokeless and black powder, to determine the chamber pressure. If you want to solve the integral equations you can also get the time-dependent solutions. These are pretty easy to do with modern software. I use mATlAB and SiMULINK for such things.

There are other volumes of the same series that describe the pressure curves and, for example, the dependence of pressure on such things as powder grain size, freebore, and barrel harmonics. QuickLoad does not account for the variances in pressure curve as a result of barrel thickness, length, etc as it relates to the harmonics, BTW.

I’d be happy to include all the equations, but it is better if you examine the documents for yourself and work the math for yourself. It's an enlightening experience.

For example, the equations clearly explain why a "short headspace" will most definitely NOT result in a catastrophic failure and stock splitting as asserted in another thread.

There are also many good discussions of this topic in other forums, most notably “Shooter’s Forum”, an example is

http://www.shootersforum.com/handloa...up-vs-psi.html

Regarding PSI and CUP, this is interesting…
http://www.shootingsoftware.com/ftp/psicuparticle2.pdf

Although Mr. Bramwell’s approach is not entirely correct, it’s a good start. My own conversion from PSI to CUP takes the form of a 3-parameter power relationship…


P.S.I. = a * (C.U.P) ^ b + c

Coefficients (with 95% confidence bounds):
a = 4.172e-06 (-1.993e-05, 2.828e-05)
b = 2.128 (1.603, 2.653)
c = 1.544e+04 (1.086e+04, 2.001e+04)

Goodness of fit:
SSE: 6.03e+08
R-square: 0.9516
RMSE: 3883

This equation can be inserted into Excel for example with good results. applies to SaamI only, the CIP takes a slightly different form due to the differences between SaAMI and CIP with regards to their respective methods.

In any case, hope you have a good evening…

JWB

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Old December 13th, 2012, 06:57 AM   #74
Platoon Commander
 
Join Date: Apr 2011
Location: South
Posts: 442
Quote:
Quote:
Quote:QUOTE]Kudos jbrooks, not only am I impressed with your integrity but also the information you posted and how you validated the facts about the function of the bridge. Your comments are very well supported with measurements and pictures. I think that your posts are very informative to those of us who don't approach the topic with preconceived notions and ridiculous conspiracy theories.
So I Consider you to be a man with whom I can reason and exchange ideas. I’m not trying to be an ass, nor am I trying to be an “alpha male’ as one of our more recent members rather clumsily tried to insinuate.
[/QUOTE]

He is only "praising you" for agreeing with him. After he and another "big dog" beat you down on the so called "safety bridge" debate.

I am not being praised because I still don't agree with them. I have "preconceived notions" after having out of battery slamfires with the sensitive primers he recommends. And I get chased around on this forum, being discredited because I had slamfires. Apparently it is OK if Big Dogs drop on on a discussion with nothing to add but slander. But my link to it is wiped out because it violates forum rules.

Quote:
For example, the equations clearly explain why a "short headspace" will most definitely NOT result in a catastrophic failure and stock splitting as asserted in another thread.
After I bowed out of that thread, the total volume of personality cultism, pseudo science, fantasy facts, and disingenuous statements being too tiring to handle, I got to talk to a bud who is working on the M2A1 50 caliber product improvement program . One thing in that program is a quick change barrel. The prime is Boeing, Lockheed, or some other big name Defense Vendor, I forget the exact one.

There are many here who know a lot more about the Ma Deuce than I, I only know what I see in books or get hearsay, owning a full Auto 50 is too expensive a proposition for me. Anyway the quick change barrel idea apparenty involves a barrel that can be put into every M2, one rotation and it is in, and the chamber headspace is correct after that one rotation. As I heard, the old M2 requires putting a headspace gage in the barrel and rotating the barrel to set headspace. The newM2A1 system requires a special ”locking” shoulder, similar in function to a FAL locking shoulder to be installed in the receiver. Supposedly once the special locking shoulder is installed the headspace of the gun is correct with every quick change barrel.

It is not turning out that way. My friend has seen many M2’s that were blown up due to excessive headspace. He has also seen what happens when the headspace is insufficient.

Unlike what you would expect from the pseudo science prognostications by the Big Dogs, what happens is that the M2’s run slow. The cyclical rate is reduced. This is due to all that case friction in the chamber as the gun has to crunch fit the case to the chamber and then, after firing, there is a unfortunate interference fit that has to be overcome. I explicitly asked, “do short chambered M2’s blow up?” and the answer was a clear *** No!

My friend also made the comment that he did not understand why every military small arm did not have a fluted chamber. Fluted chambers break the friction between case and chamber, improving function. I don't know, chamber flutes are in the most advanced weapons designs and even legacy designs should benefit from them.





Last edited by slamfire1; December 13th, 2012 at 07:34 AM.
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Old December 13th, 2012, 08:27 AM   #75
Grunt
 
Join Date: Sep 2012
Location: Texas
Posts: 105
i have a PTR-91 with a fluted chamber. the friction is not reduced, it is amplified. if i use a softer shell like brass, when the case expands during firing, the brass will dig in to the grooves of the flutes and the ridges of the flutes dig into the brass, thus creating a heck of a lot more surface area in the chamber and a lot more drag during extraction. if i use brass cases with that gun, i can get through about 20-30 rounds before the chamber becomes bassicall welded shut, if i wait about 20 minutes, i can open the chamber, but with in 5-10 rounds i have the same problem.

if i use something a little bit harder and with more tensile strength, like steel cases, i can punch holes with that thing all day long.

there is no operating rod in a PTR-91, it's the exact same operating mechanism as the G3, HK-91, MP5... most HK long guns. the chamber is opened by the gasses moving past the chamber and applying their force to the bolt face pushing it back forcing a pair of roller nuts inside to push a locking piece rear ward. it makes for a very dirty gun at the end of the day. fun to shoot, but i pay for it later.

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