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Discussion Starter #1
I Wish All a Happy & Safe Memorial Day Weekend.

I would like to know what you all are seeing as far as shoulder push/expansion on your fired cases.

I have a RCBS Mic that I trust as it verifies against a known chamber and my Hornady tools as well.

I am seeing an average shoulder push of about .015 on my fired brass. It is pretty dog gone consistant.

What are you guys seeing on your fired cases?

My 308 bolt gun is dead nuts on at 1.630. Fire formed cases come in at 1.628 - 1.629 with most being 1.629. That's how I know that my RCBS mic is dead on.

I guess a .015 push on the shoulder is why these M1A/M14 rifles are tough on brass. I pretty much have assumed that and I am annealing the brass.

Looking forward to hearing from you all.

Happy Weekend to All of My Brothers out there.

Ole Silver
 

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I assume from what you wrote, that your cases come out long after firing. Much longer than what you get from your bolt rifles.

First of all, remember for this rifle and all military semi automatic rifles, reloading was not a consideration. The nation that issued this rifle gave nice new ammunition to their Soldiers and those guys were not expected to police up their cases in combat. Now at the shooting range, yes, there is brass turn in, but for scrap, not reloading.

Your rifle is acting as it was designed. I am unaware of a single gas operated semi automatic mechanism that does not stretch the brass something awful.

M1a’s unlock when there still is residual pressure in the barrel. LTC Chin’s book call it “the residual blowback effect”, or something like that. This pressure is there to help keep the mechanism going after unlock. The pressure has to be low enough so that at unlock the case does not rupture. That value is around 650 psia for 20mm, again from Chin’s book.

That little inset in this AMCP diagram shows the pressure drop for a 308 round. That will inset is in there because this is an important design consideration in the timing of the rifle. Not too slow, not too fast.

As your rifle unlocks, lets say below 650 psia, the front of your case is still glued to the case walls. When a M1a extracts, it pulls on the cases, and as long as the case is sticking to the sidewalls, it gets stretched.


Roller bolt actions open so faster and early in the pressure curve that cases were being ripped apart. The Russians figured out to flute the chamber, the Germans copied it, and it is in all the HK91 actions. This action floats the upper 2/3 rds of the case off the chamber walls, the back end is the gas seal. I don’t think my PTR 91 cases get stretched longitudinally, but they might be wide around the middle. I will have to check that.

You can reduce case stretching in Garands/M1a’s if you leave the case lube on your cases. This is assuming you are not shooting overpressure loads. I have been doing this for over a decade on the suggestion of a Distinguished HM gunsmith. He said you could take your cases an entire shooting season, and he was right. I took one set of 100 LC cases 22 reloads and never had a case head separation. I just set the shoulder back .003” from the chamber on each full length small base resize.
 

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Hi Old Silver,

I use the RCBS mic too I like it, started using a Redding Instant indicator....same principle but I can check cases much quicker :)

But yes to your question, when I check fired LC brass from my rifle, my RCBS mic shows typically +2 hashes on the RCBS mic(meaning the shoulder has moved forward +2 notches from my base line...I dont want to say .002 of an inch because thats technically not correct since the RCBS mic is a comparitor, not a measuring device.

But you get the idea yes + 2 marks on the RCBS mic and this varies a touch every now and then.
 

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So is the case stretching due to too much pressure in the chamber when the bolt starts to unlock? Or do you have a chamber with more headspace than what you would think is normal?
Two different problems that would need to be addressed differently.
If the chamber of your M1A is on the large size you'll need to re-size your brass accordingly. Annealing the brass won't help the brass much. While it will keep the shoulder and neck from cracking the brass will still fail back near the case head.
There was an ROTC cadet that used to shoot high power with us civilians with an M14 the Department of the Navy issued to him. That rifle had a long chamber and the cases where also stretching 0.015". He was getting case head separations on the 3rd loading of his brass. After we confirmed that his chamber was large he started re-sizing his brass by just setting the shoulder back about 3 thousands. Problem went away. You'll probably have to keep those rounds away from your bolt gun chambers as they will be long for them.
If the powder your using is too slow for the proper functioning of the M1A it's time to switch powders.
 

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Discussion Starter #6
Thanks to those who have responded with very good information.

The question is, are you seeing .015 shoulder push when you check your brass fired from an M1A/M14?

I have observed this with LC, GGG, WIN & IVI brass.

My stripped bolt will close on 1.631 & be very tight on 1.632.

Fired brass comes in at 1.645-47.

I size to 1.628-30.

I'm charging with IMR4895 or IMR4064 depending on what I'm doing & with what I'm doing it with.

Thanks,

Ole Silver
 

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DO NOT lubricate your finished cartridges as a standard reloading procedure, that increases the bolt face pressure by several thousand PSI. No government or private institution or firearms/ammunition manufacturer recommends lubricating cartridges, SAAMI, the NRA, Springfield, the military, and all major firearms manufacturers state that you should never lubricate your loaded cartridges.

The case is designed to stick to the chamber walls, sticking to the chamber walls transfers force/pressure to the rifle's chamber. If you lubricate the cases then that force will be transferred to the bolt face rather than the chamber walls. That bolt face pressure (called back thrust) will increase the force applied to the bolt lugs. The end result is that the receivers and bolts will stretch over time. I'm not saying that the rifle will self destruct the first time you fire a lubed case but I am saying that the rifle's life will be shortened. All metals accumulate forces, and over time, those forces will cause stress fractures. The greater the forces you subject the metal too the sooner the stress fractures will occur.

As for the stretch of your cases, that all depends on how you adjust your resizing die in relation to the chamber's headspace dimension and the op rod dwell time. Using the proper powder also helps control case stretch. I use Lapua brass quite often and they measure 1.623" at the shoulder's headspace datum point. When I fire them they will stretch to different lengths depending on which rifle I fire them in. The SOCOM will stretch them to about 1.633" and the loaded will cause them to measure about 1.631" at the shoulder, and yes, they match my chamber headspace dimensions very closely. These numbers are based on virgin brass, on subsequent loadings, I usually only get a few thousandths of an inch of stretch because I resize the brass to 1.629". So with virgin brass I get about 0.010" stretch and after that I get about 0.004" stretch.

Now I would also like to point out that I've adjusted my op rod dwell time so that the bolts open later than they did when the rifles were new. That gives the case a little time to cool off and not be as elastic when the bolt yanks them out of the chamber. I'm sure that this helps reduce the amount of stretch that I get.
 

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I have to go with Rammac on the no case lube....all that pressure is transferring straight bace to the bolt and the locking lugs with a lubed case. Makes me nervous to consider that with a milled receiver...... and especially with a cast receiver. (I can buy more brass...eyes are irreplaceable).
 

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I noticed what Ole Silver posted about once fired brass from rounds shot out of my M1A. I understand that is the nature of the beast with shooting a semi-automatic rifle. What Slamfire1 posted is a great explanation of why this occurs.

I wander what the difference is with my semi-automatic Rock River Arms LAR-8, because once fired brass measures the same as out of my bolt action target rifle. It drops right in to my loaded cartridge headspace gauge and comes back out without any force.
 

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Discussion Starter #10 (Edited)
RAMMAC,

I do not lubricate my finished ammo. It is tumbled clean after resizing.

As for dwell time, I think you are onto something there. I have messed with the gas plug in the past and this may be where I messed up. I'm gonna get a new gas plug.

How are you setting the dwell time on your M1A's?

Also, I am wondering if freshly annealed brass will stretch more on the first firing?

Thanks,

Ole SIlver
 

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I adjusted the dwell time by taking material off the gas plug, I'm sure I went through the hardened metal and I didn't re-harden it so I'll be buying new gas plugs in the near future but that doesn't bother me. I did the work just to see what would happen, next time I'll re-harden them. As for how I adjusted the dwell, I took metel off of the plug's face (the end toward the gas piston) until the gas plug only required 3/4 to 1 full turn to tighten by hand (I finish tighten with a torque wrench).

I don't know for sure if freshly annealed brass would stretch more but it seems to reason that it would. I don't anneal my brass so that could be another factor causing a difference between your amount of stretch and mine.

I'm not sure of all the factors that effect the case stretch but I do know that some load recipies seem to cause more stretch than others, and I'm not talking about high pressure loads. I think it has something to do with the pressure/time curve. Maybe some powder burns retain too much pressure late in their burn and that higher pressure still exists when the bolt starts to extract the hot case. I'm sure that slamfire is correct about there being some residual back pressure at the moment of extraction and I suspect that it's possible to get that pressure too high.


RAMMAC,

I do not lubricate my finished ammo. It is tumbled clean after resizing.

As for dwell time, I think you are onto something there. I have messed with the gas plug in the past and this may be where I messed up. I'm gonna get a new gas plug.

How are you setting the dwell time on your M1A's?

Also, I am wondering if freshly annealed brass will stretch more on the first firing?

Thanks,

Ole SIlver
 

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Discussion Starter #12
RAMMAC,

Thanks for the info on the gas plug mod. I did the exact same thing. I've set mine so that there is .016 between the gas lock and the front of the locking surface on the gas plug. That's about 3/4 of a turn to lock up.

I'll let you know how the brass stretches on the 2nd firing after being annealed.

My loads are nothing special. 4895 & 4064. Never more than 42 grains with 150g pills and usually about 41 grains with 168's. Usually loaded at 2.825 length.

I'll let you know what happens.

Thanks,

Ole Silver
 

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DO NOT lubricate your finished cartridges as a standard reloading procedure, that increases the bolt face pressure by several thousand PSI. No government or private institution or firearms/ammunition manufacturer recommends lubricating cartridges, SAAMI, the NRA, Springfield, the military, and all major firearms manufacturers state that you should never lubricate your loaded cartridges.
These are all magpies repeating what the parrots told them. Remember the motto of the Royal Society: “Nullius in Verba”, “on the word of no one”.

Knowledge about the material universe should be based on experimental evidence rather than authority.

I had heard similar stuff and yet, in front of me at matches, was a gentleman who had been leaving the case lube on his M1a’s for years. According to the magpies his rifle should have blown into pieces, and yet, the physical evidence in front of me was, it did not.

This caused me to search for how rifle mechanisms are designed and it was very interesting search.


The case is designed to stick to the chamber walls, sticking to the chamber walls transfers force/pressure to the rifle's chamber. If you lubricate the cases then that force will be transferred to the bolt face rather than the chamber walls. That bolt face pressure (called back thrust) will increase the force applied to the bolt lugs. The end result is that the receivers and bolts will stretch over time. I'm not saying that the rifle will self destruct the first time you fire a lubed case but I am saying that the rifle's life will be shortened. All metals accumulate forces, and over time, those forces will cause stress fractures. The greater the forces you subject the metal too the sooner the stress fractures will occur.
A couple of questions:

Is the brass case a structural element, that is supposed to carry load, or is it a gas seal, something that must be supported?

Is the brass case working above yield or below yield?

What load is the receiver designed to support? The full load of the cartridge?, or is the action weakened, assuming that the case carries some of the load?

I have to go to bed for a rifle match tomorrow, maybe later.
 

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Here's some interesting evidence, slamfire1 picked his forum name because he's had a couple of slamfires. Additionally, the high pressures that are caused by lubricated cartridges can knock the receiver out of spec and one of the causes of a slamfire is an out-of-spec reciever.

So, the person who lubricates his cartridges has had a couple of slamfires and the guy who doesn't lube his cases has never had a slamfire with any of the three M1As that he owns, and one of those rifles is 30+ years old, has had many thousands of rounds through it, and it has all the original parts.

Ya'll can do the math and make your own choice.
 

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Discussion Starter #15
I don't leave case lube on loaded rounds for one very simple reason.

The lube collects foreign matter and I don't want that in my chamber. I also don't want it in my magazines. I really don't want may fingers getting lubed when I load the mags.

I am meticulous about keeping my dies and other tools clean too. That crap builds up and causes all kinds of problems.

Slamfire, with all due respect, I am not going to change what I am doing. I just wanted to know what other members are seeing as far as how far thier cases are stretching with relation to the headspace/shoulder push.

RAMMAC, Thank you for answering my question.

To everyone else, the question still stands.

How far are the shoulders of your cases being pushed out? I have a firm grasp on why they are stretching and expect them to stretch.

On another note, On this very special weekend, my profound thanks and respect to those who have given all in the name of freedom. May god bless these patriots.

Captain Isaac Davis of the Acton, MA. militia when asked if he would lead the Minutemen into battle at the old Concord Bridge on April 19th 1775. He was one of the first to die taking a musket ball directly to the heart.

"I have not a man who is afraid to go".

Ole Silver
 

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I've been thinking about your question especially in light of the fact that I just happened to be working along the same lines recently (asking myself what is the best headspace dimension) and I've been doing some experimenting.

The one conclusion I've come to is that my virgin Lapua brass seems to provide the tightest groups and never shows pressure signs unless I load them to the absolute hottest that I can. The interesting thing is that the virgin Lapua brass averages 1.623" at the shoulder datum line.

One other general observation is that the SOCOM had greater variation in the case dimensions and it has the longer chamber headspace dimension. Since I used the same headspace dimension while preparing all of the cartridges, that means the the case headspace was only about 0.002" less than the Loaded model's chamber headspace while the cases were about 0.004" shorter than the SOCOM's chamber headspace.

And a finally, none of the reloaded cartridges gave me as tight of groups as the virgin brass did. I think that this might be a result of neck tension. The necks are longer on the virgin brass. After firing the first time I trimmed the cases to 2.003" (they varied between 2.002"-2.003"). I remember trimming them only because that is the length I have been using recently, not because they were longer than spec. I think I need to test the neck tension theory in the future.

Now I've always been taught to resize my cases to about 0.004" short of my chamber's headspace for best accuracy but when I recognized the fact above, I talked with a gunsmith/bench rest shooter that's a friend of mine. He said that bench rest shooters have recognized for some time that some rifles perform better with more room between the cartridge and the chamber. He described it as allowing the case to be in a more relaxed state since there are no stresses due to contacting the chamber anywhere except at the bottom where the cartridge is lying.

All this has led me to start testing different headspace dimensions to see if there is a "best" performer.

Over my years of reloading ammunition, I've noticed that there seems to be a best headspace value that works better than others in regards to limiting case stretch. Unfortunately I've never monitored that dimension because I haven't been interested in that kind of precision until now. I'm wondering if there is some kind of "sweet spot" value that will cause the rifle to shoot it's best while reducing stretch. I'm thinking that if I find this to be true and you combine this info with a light load, I might just have a nice balance between accuracy, precision, and light loads that allow the rifle and brass to last longer.

I hate to waste forum space but maybe this will stir some comments and push an answer to your question. Here are some graphs I've done so far comparing how the brass has changed from virgin condition to fired twice. I resized in between using a Redding neck sizing die ( I know, it's not supposed to be done, but I did it in the interest of not changing the brass any more than necessary, and I did check each piece of brass to ensure that they would chamber properly) and I fired each cartridge with the gas system turned off.

Loaded Model M1A Tests




SOCOM 16 Model M1A Tests


 

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I don't leave case lube on loaded rounds for one very simple reason.

The lube collects foreign matter and I don't want that in my chamber.


Which is one of the reasons oilers were undesirable and eventually were designed out of semi automatic mechanisms. The use of oilers is beyond living memory so this may come as a surprise to some.

This Italian Breda used an oiler, and that is an oil tank on top:

http://historywarsweapons.com/breda-m30/

This Japanese Nambu type 11 has an oiler tank on top. On your way to Camp Perry this year stop on by the Cincinnati Union Terminal and see this display.
http://www.cincymuseum.org/unionterminal


http://www.forgottenweapons.com/light-machine-guns/type-11-nambu-lmg

The Schwazlose used an oiler, there are really good Schwarlose pictures at this site, along with a description of the oiler.

http://www.gotavapen.se/gota/artiklar/utv_ksp58/ksp14/schwarzlose.htm

It was difficult to design out oilers prior to WW2. Pedersen offered ceresin wax for use in his 276 Pedersen rifle, but that was turned down. Everyone can read that in Hatchers Notebook and the short descriptions of oilers in the rifles tested by the Army prior to the adoption of the Garand.

Since WW2 gas flutes have replaced oilers in a number of service weapon designs. Gas flutes perform the same function without having an oil tank, drip mechanism, and the need to carry oil cans into combat. Note that the lower third of the case is the gas seal, the upper 2/3rds is floated off the chamber walls.



WW2 steel cased ammunition caused excessive breech friction in many US service weapons, causing malfunctions. Steel was cheap, cheap is good, so the US Army tested dry film lubricants in the 50’s. These tests included steel case 30-06 rounds which would have been used in every issue 30-06 of the period. The Garand was in service at the time, remember? The American Rifleman said the cost of lubricated steel cases exceeded the cost of brass so the whole thing was eventually scrapped.

This is from AMCP 706-260 “Automatic Weapon Design”



There are modern actions that use dry film lubricants on their cartridges. These dry film lubricants are necessary for function and safety. I read a post about people being injured when reloading for the FNPS 90. They lost the Teflon coating off their fired cartridges but how that might lead to an injury, I don’t know.

The FNPS 90 is an interesting concept:

 

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Discussion Starter #19
Here We Go Again...

Slamfire & D308FAM,

The data that you present, not to mention the verbose nature of same, I found entertaining and educational to a point.

My loaded stuff is clean & not lubricated. That's it & that will not change.

I enjoyed reading and then realized that I was not getting an answer to my question.

Can either one of you tell me how much your brass stretches out?

When I ask someone where I can go to take a leak, I don't need a travel agent.

RAMMAC - I have a 1968 SAK GI contour barrel and was wondering if maybe the way it was cut may be the reason I am getting more stretch.

I love this forum and don't want to p-ss anyone off but I asked a simple question.

Ole Silver
 

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RAMMAC - I have a 1968 SAK GI contour barrel and was wondering if maybe the way it was cut may be the reason I am getting more stretch.
Actually I'm having the same thoughts as you are but I'm not sure if it's the way the chamber was cut or just the way we are trying to size the cases to match the chamber.

Looking at my earlier post, I know that the SOCOM has a loose chamber compared to my loaded and knowing that makes it easy to understand why the cases shrink more after firing. The case has a specific amount of material and more of it stretched out in circumference rather than the length. Maybe that means that you need to bump the shoulder back more on your cases in order to give the case room to expand from the base to the shoulder rather than expanding from the shoulder to the mouth.

Oh, I almost forgot, you did notice that I did those case tests with the gas system off didn't you? I need to run the same test with the gas system on and compare the difference.
 
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