Chamber shoulder and case shoulder gauge for .303?

[Edward Horton]

The AG-42 Ljungman was a gas operated rifle designed from the ground up to use 6.5x55mm lubricated ammunition and the Model 1894, Model 1896 and Model 1938 Mauser type manually operated bolt action rifles did not require lubricated ammunition and were designed to operate without the use of lubricated ammunition.

The key words here are designed to operate “with” or “without” lubricated ammunition and NOT “I think it is OK” to use lubricated ammunition with its increased bolt thrust.

Ag m/42

The Automatgevär m/42 (Ag m/42) (outside of Sweden commonly known as the AG42, AG-42 or Ljungman) is a Swedish semi-automatic rifle in limited use by the Swedish Army from 1942 until the 1960s.

Operation

The Ag m/42 is operated by means of a direct impingement gas system, similar to that of the French MAS-49 and American M16 rifles. The Ag m/42 also uses a tilting breech block like the Tokarev SVT-38 / SVT-40 and FN FAL rifles.

The Ag m/42 uses the 6.5x55mm cartridge loaded into a removable 10-round box magazine. In practice, however, the magazine usually remains attached to the rifle while it is loaded from the top with five-round stripper clips. Like the British Lee-Enfield and Soviet SVT-40, the Ag m/42's magazine was intended to be removed only for cleaning.

Use caution when firing the Ljungman and Hakim rifles as the burn rate of the powder has a dramatic effect on the operation of the rifle. There have been reported cases of catastrophic failures of both these rifles when fired with incorrect ammunition. Even the Swedish m/41 ammunition was required to be lightly oiled by Swedish troops prior to loading as the burn rate of the powder is too slow and the oiling of the cartridge body facilitates extraction.

The main dynamic involves the pressure curve and the timing of the pressure curve as it relates to the location of the gas port in the barrel. While the Hakim has a gas port adjustment the Ljungman does not. As the bullet passes the gas port the gas pressure is channeled back to the bolt carrier to unlock the bolt. With a powder that is too slow a burn rate the bolt carrier opens violently prematurely and at an extremely excessive pressure. This causes the extractor to tear the rim off the cartridge case exposing the action to the dumping of very high pressures which typically exits the action downward into the magazine well, blowing the magazine completely out of the rifle and often destroying the magazine and stock in the process. Close attention must be paid regarding the use of correct ammunition in these two rifles.

Ag m/42 - Wikipedia, the free encyclopedia

[Edward Horton]

Sometimes I wonder what people are thinking when they decide to cheat and bend the rules on gun design and cause possible gun damage and accelerate wear on a rifle designed to shoot ammunition that is not lubricated..

The Enfield Rifle has already been labeled “an inherent weak design” and an action that flexes due to its rear locking lugs, WHY on earth would anyone want to lubricate a cartridge case in the Lee Enfield rifle and cause TWICE the force to be delivered to the bolt face and twice the damage and wear this rifle was designed to receive is beyond me.

I spent the last 25 years of my career as an Inspector at a military overhaul depot and it never fails to amaze me how many people ignore warnings and instructions in the manuals because they “think” they are “smarter” or “know more” than what is printed in the manuals.

97% of all errors are human errors and only 3% are actual mechanical failures and egos and assumption are the major cause of mechanical breakdowns and component failures and this is what causes aircraft to fall out of the sky.

[Bindi2]

I am beginning to think that there are vested interests at work on this thread to keep the focus off the issue of either brass composition used in case manufacture or the manufactureing method used which is causing a problem with head separation in some Lee Enfields.

[Edward Horton]

Bindi2

Our American or SAAMI made .303 cases could be made correctly to these standards and the larger chambers of the Enfield could be directly responsible for the short case life. BUT I think other factors could have something to do with the short case life when reloading.

Most of my questions are related to and come from reloading commercial ammunition in my Springfield 03-A3 with its corresponding larger military chamber and headspace and the 30-06 cases lasting far longer than currently made .303 cases.

The problem at Gunboards was my postings concerning cases life, chamber pressures and reloading methods kept getting locked down or the entire post deleted because of arguments from our online internet engineers.

What bothers me the most is the set piece standard answers about the “inherent weak design” or the “action flexing” on the Enfield and the fact no one wants to think outside the box and look at other contributing factors on case life.

And then to add insult to injury when your posts on fire forming cases using o-rings are hijacked by cartridge case oilers, who think they are the only ones in the world who know how to reload, you never get anything accomplished on the subject.

When I look at a 2002 Canadian Enfield manual and see headspace standards that are written for a cartridge case that is to be fired once, which translates to .064 GO, .070 NO-GO and .074 Field I wonder what has changed and why.

(I keep thinking it might be the brass case and the standards used to make them)

[ireload2]

#4 MK1 Lee Enfield bolt and receiver deflections at a given PSI

These are real numbers.
These numbers can be duplicated in Excel if you are interested.
The formulas and techniques are readily available on the internet.

All dimensions are in inches, pressure in PSI.
Note the deflections translate into stretching of the pressure ring
when the case body adheres to the chamber wall and the case
head is pushed against the bolt face.
I personally think it is poor practice to use case head stretch as a mechanical brake to minimize load on the action. Everyone that cleans a gun usually fires a shot or two with oil in the chamber each time they go to the range.


.......................Receiver.......Bolt........ .Total Deflection***
...PSI............... Stretch....Compression Receiver+Bolt
30000................0.0009.......0.0037.......0.0 046
35000................0.0011.......0.0043.......0.0 054
40000................0.0013.......0.0049.......0.0 062
41440................0.0013.......0.0051.......0.0 064
45000................0.0014.......0.0055.......0.0 069
50000................0.0016.......0.0061.......0.0 077
55000................0.0017.......0.0068.......0.0 085
60000................0.0019.......0.0074.......0.0 093
65000................0.0020.......0.0080.......0.0 100
70000................0.0022.......0.0086.......0.0 108
75000................0.0024.......0.0092.......0.0 116
80000................0.0025.......0.0098.......0.0 124
85000................0.0027.......0.0104.......0.0 131
90000................0.0028.......0.0111.......0.0 139
95000................0.0030.......0.0117.......0.0 147

[ireload2]

The Lee enfield requires a certain amount of friction grip between the case and chamber to reduce bolt thurst, oiled cases where used to limit the friction to check to see if the lugs were correctly where they should be before the Goverment inspector passed the rifle for Goverment ownership. British Goverment requirement. Machine guns do not require that friction many will not operate with sticky cases hence oil on cases.

Do you have citations for your assertions?
What is the certain friction grip? Is it quantified? What happens if you clean your and oil you gun with PTFE lubes?
This friction grip is modified by polishing your brass. It can also be modified by polishing your chamber. Are you also implying that you should not polish your brass or the chamber?
All rifles inevitably get fired with some oil in the chamber.
Are you saying this will damage a Lee-Enfield?
Is that why Lee-Enfields seem to have such gross headspace?

Do you have answers for any of this?

[ireload2]

Posted by EH

>>>Springfield 03-A3 with its corresponding larger military chamber and headspace and the 30-06 cases lasting far longer than currently made .303 cases.<<<

You can easily measure the Springfield receiver and bolt that permit you to calculate the stretch of the receiver and the compression of the bolt.
If you will do this once for the Lee-Enfield and once for a front locking bolt gun you will have a lrge part of your answer. There is no magic.

[ireload2]

Posted by Parashooter.
>>>I believe those who assert that radial expansion contributes to the kind of head separation commonly encountered by .303 reloaders are mistaken. Radial expansion puts the circumference of the solid case web in shear, not stretch - and it does so in a completely different location.<<<<

The case pressure ring material has to stretch radially until it it constrained by the chamber. There is some bending since the stretch occurs at an angle due to the proximity of the solid head. However this still results in the pressure ring being stretched buy the difference in diameter of the case and the chamber as well as the forces that stretch the case along it's longitudinal axis. Stretch along the relatively long longitudinal axis has the opportunity to get spread over a long portion of the case length. The radial stretch that occurs to the pressure ring area is concentrated over a short distance increasing it's damage to the case wall. If there was no stretching caused by the difference in diameters it would be possible to use a much smaller cases head with no consequences. We know that is not possible.

[ireload2]

[QUOTE=Edward Horton;54858]Sometimes I wonder what people are thinking when they decide to cheat and bend the rules on gun design and cause possible gun damage and accelerate wear on a rifle designed to shoot ammunition that is not lubricated..

The Enfield Rifle has already been labeled “an inherent weak design” and an action that flexes due to its rear locking lugs, WHY on earth would anyone want to lubricate a cartridge case in the Lee Enfield rifle and cause TWICE the force to be delivered to the bolt face and twice the damage and wear this rifle was designed to receive is beyond me.

I spent the last 25 years of my career as an Inspector at a military overhaul depot and it never fails to amaze me how many people ignore warnings and instructions in the manuals because they “think” they are “smarter” or “know more” than what is printed in the manuals.

97% of all errors are human errors and only 3% are actual mechanical failures and egos and assumption are the major cause of mechanical breakdowns and component failures and this is what causes aircraft to fall out of the sky.<<<


Interesting to think that an inspector thinks he knows more about the rules than the engineers that make them.


All errors are human errors. BTW manuals are full of errors. Even inspectors have an error rate. The only way to stop errors is to kill all the people.

You lubricate the case so you don't use the case as a mechanical brake.
Using the case as a mechanical brake guarantees damage to the case. To avoid damage to the action reduce the loads. You can't stop it from flexing.

[Patrick Chadwick]

Dear All, let's keep calm.

I am getting worried. I am trying to learn something from other people who have knowledge that I do not possess, but have the increasing feeling that merely asking why or how is sufficient to cause offense. If that is the case, then the forum will not function in the sense of a profitable exchange of ideas and information.

I am grateful to be able to read contributions that provide facts and experience that I do not have and cannot otherwise acquire. I was a development engineer and then head of a development laboratory in a very large international company for many years. An activity that requires that you know the book, before you start, but also that you are prepared to investigate some of the assumptions in the book, without that being considered frivolous or those who wrote the book becoming offended. I would like to see the forum progress in this spirit

In the case of the rear-locking bolt construction of the Enfield, I am charmed by the brilliant simplicity of the O-ring method, and will try it out when the competition season has tapered off.

But a thought occurs - assuming that ireload2 has used the correct modulus of elasticity etc, then we are faced with the following limitation: even if we have an Enfield action with a zero headspace, then, if the case head remains in contact with the bolt head, the case head will be pushed back as the bolt is compressed, and then pushed forward as the pressure drops. So a case that has been held up against the bolt face with an O-ring will, after firing, have undergone a rapid cycle of stretching and compression by the amount of the bolt compression, even if all other play is zero.

In other words, the rear locking bolt system is going to strain the case even if there is a perfect case-chamber match. And the only way to reduce that effect is to reduce the pressure peak. So while I am sure that the O-ring method is a very good idea to reduce the cartridge strain, and should therefore increase case life, there will still be a strain cycle that will, eventually, cause the cartridge to fail. It would therefore be interesting to hear if there is any data on 303 cartridge life using the O-ring method.

Patrick