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Reloaders - 7.62/308 Shoulder Expansion Info.

This is a discussion on Reloaders - 7.62/308 Shoulder Expansion Info. within the Ammunition forums, part of the M14 M1A Forum category; 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 ...


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Old May 26th, 2012, 01:12 PM   #16
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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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Old May 26th, 2012, 03:12 PM   #17
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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/ligh...e-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/artikla...chwarzlose.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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Old May 26th, 2012, 04:06 PM   #18
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Last edited by D308FAM; May 26th, 2012 at 08:25 PM. Reason: Complaint - Not to the posters point.
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Old May 26th, 2012, 07:08 PM   #19
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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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Old May 26th, 2012, 08:01 PM   #20
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Quote:
Originally Posted by Ole Silver View Post
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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Old May 27th, 2012, 02:37 AM   #21
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I chamber my M14 rifles right in the 1.632 range. My brass case headspace is set at 1.628. After firing cases stretch approximately .006 to .008 or right in the 1.634 to 1.636 range. All lube is removed from cases after loading. Been doing it the same way for 46 years with no troubles. Mil brass,current load used 41.5 4895 CCI #34. 168 smk.

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Old May 27th, 2012, 07:18 AM   #22
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Quote:
Originally Posted by nf1e@snet.net View Post
I chamber my M14 rifles right in the 1.632 range. My brass case headspace is set at 1.628. After firing cases stretch approximately .006 to .008 or right in the 1.634 to 1.636 range. All lube is removed from cases after loading. Been doing it the same way for 46 years with no troubles. Mil brass,current load used 41.5 4895 CCI #34. 168 smk.
Thank you for this info. I wish I was seeing .006 to .008 stretch but mine is more like .012 - .016

Your load is one of my favorites too although I am going to try Fed GM210 primers.

RAMMAC - My gas system is unitized so I don't have the option of shutting it off to test.

Thanks,

Ole Silver

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Old May 27th, 2012, 09:59 AM   #23
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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
Fair enough, I was answering attacks not your needs.

I took my bag of LC66 brass, the brass I fired 23 times in my M1a, last time I shot this was during Rattle Battle at Camp Perry, then I decided to retire the brass because primer pockets were getting large. This brass was last lubricated with Johnson Paste wax, as paste wax leaves a dry coating, it is a dry film lubricant. I suspect the wax is ceresin wax, the same stuff used in the Pedersen rifle.

I dropped the unsized cases into my Wilson gage. The top step corresponds exactly to a No Go chamber gage at 1.634” The lower step is 1.630”. All of these cases show a shoulder expansion above the “No Go” ledge. I small base size to gage minimum (1.630") , plus or minus, for my gas guns, to ensure reliable function and minimize the chance of an out of battery slamfire.



The barrel this brass was shot in has been long used up, I am on the third match barrel for this rifle. I don’t remember the chamber headspace of that barrel. You can assume it was cut with a pull through reamer, it may have been a minimum chamber. I ask for Go plus two, but gunsmiths use what tools they have and you get what they give you.

So you can see that this brass has been stretched about 0.019” from "Go".

Even so, this stretching is not coming from the case head as I have sectioned some of this brass and never, ever, ever, saw evidence of case head separation or brass necking in the sidewalls even though this brass has been fired 23 times in M1a's.



I tried several calipers and there is error in measurement and slight differences in caliper readings. Don’t assume that my gages have been to cal lab recently or these measurements are definitive.


Thanks from Ole Silver
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Old May 27th, 2012, 10:45 AM   #24
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Slamfire1,

That is some very good information.

23 times fired, wow!!!

Do you have to resize the case neck to get it to drop into the Wilson gauge? The reason I ask is that I have a Lyman gauge & I have to resize the neck before I can get a meaningful measurement as the case neck gets stuck in the gauge. After neck sizing, I am seeing very much the same thing that you are seeing but mine are not going out quite as far. I am seeing an average of about .015. That is on twice fired brass that was annealed before the second firing.

Do you anneal your brass?

Thanks for the great info.

Ole Silver

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Old May 27th, 2012, 12:41 PM   #25
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Do you have to resize the case neck to get it to drop into the Wilson gauge? The reason I ask is that I have a Lyman gauge & I have to resize the neck before I can get a meaningful measurement as the case neck gets stuck in the gauge. After neck sizing, I am seeing very much the same thing that you are seeing but mine are not going out quite as far. I am seeing an average of about .015. That is on twice fired brass that was annealed before the second firing.
I just dropped the cases, as is, in the Wilson gage. I did wipe off wax residue and powder residue from around the case necks so I would get a truer reading within the gage.

These cases were fired in a match barrel. If your barrel has a military chamber it is very likely larger all the way around. Military chambers tend to be big, they want function in all conditions with ammunition from all over NATO.

I never annealed the brass. That was something I was not willing to spend a lot of time on, I shoot something basically each weekend, so I have to get my brass loaded up and ready for the next match.

I have ammo cans of once fired LC and I do agree that annealing would prevent neck cracks, but I am willing to trade off the case loss for the time.

I have several friends who are F Class Champions, these are people who are very good rifle shots whether it be rimfire or centerfire. They start with good brass and get world class results and they don’t anneal case necks.

Ammunition errors are small compared to shooter errors. People who shoot only on concrete benches with 40 lbs of sandbags with psuedo benchrest rifles will see errors due to ammunition that you will not see in a human held weapon. That is assuming they can read the wind. It does not matter how good a rifle you have, if you want to compete well in Long Range, you better be able to read wind in print and in the braille version.

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Old May 27th, 2012, 01:16 PM   #26
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Slamfire1,

HeHe,

Point taken on the GI barrel. I have a 1968 SAK GI barrel that never saw action before SA screwed on the receiver in 1990. It works real well though.

I am expecting my new rifle just about any day now. LRB M25 with WMMW 22 inch barrel. Jon Wolfe is building it for me. From what he has told me, test firing will be next week.

I was gonna have a M1 tanker built but decided to just keep my old SAI standard in a nice tight FG stock. The build that Wolfe is doing for me is in a JAE Gen2. The SA standard did an admirable job in the JAE. The standard is now my field rifle. A good rifle to take hiking in Colorado. The Wolfe will be for long range work.

Thanks Again for your info.

Ole Silver

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Old May 27th, 2012, 02:39 PM   #27
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Ole Silver: This will sound like lecturing, but if you have brass fired in a GI barrel, for safeties sake, size it in a small base die before you use it in a commercial chamber.

Here are some pictures illustrating my concerns

I found two cases, big cases, that had obviously been fired in a GI barrel.

On the left is a Wilson gage. This gage is cut large between the shoulders so you can get a rough measurement of chamber headspace.

On the right is a reamer cut gage. This gage was cut for my by Gene Barnett after my first Garand out of battery slamfire. This was all from the school of hard knocks. Gene cut this reamer with the same reamer he uses in chambering his barrels. I have used many of Barnett’s barrels over the decades now. This reamer is dimensionally correct for a rifle chamber and as you can see, the unsized fired case will not drop into it. The other big case drops right in the Wilson gage.

By the way, if you want a reamer cut gage, you can also call Compass Lake Engineering in Florida. Frank made me one for my .223 and it was about $35.00.









Here I have sized one of these cases in a standard sizing die, it is trimmed and clean and ready to drop in.




You see here that a standard sizing die does not reduce a ballooned case enough and there is an interference fit. This amount of case sticking up is virtually identical to the interference fit I had with my 30-06 cases on my second out of battery slamfire. On those cases I had reamed the primer pockets deeply and seated all primers by hand. But those Federal primers were just too sensitive and the interference fit of the case in chamber was enough to defeat any firing pin blocking function that the firing pin retracting cam could provide. With a case this long the bolt stops, to crunch fit the thing, and the firing pin rebounds off the primer because there is nothing to block it. If this happens before lug engagement, and you have a sensitive primer, the result will be an out of battery slamfire.

I highly recommend you only use the least sensitive primers on the market, currently CCI #34’s and Tula7.62 are the only primers advertized as “mil spec”.



Here the other case, sized in a small base die, just drops flush in the reamer cut gage. This is what you want, a non-interference fit to your chamber. As Gene told me “you want the case smaller than the chamber”. He was 100% right.

Another thing, because of the reamer cut gages I have, I have noticed that cases that fell into the gages after sizing, will sometimes be an interference fit if they are crimped. Crimping buckles the shoulder or case neck, I don’t know what because the effect is too small to see, but it does something. I do not recommend crimping bullets for that, and a number of other reasons.

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Old May 27th, 2012, 04:06 PM   #28
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Slamfire1,

Thanks for the coaching.

Fact is that I have brass for each of my rifles.

I have not found any need to use small base dies.

I body size with a Redding die and then neck size with either a Lee collet neck sizer or a Forster bushing bump neck sizer. It all depends on what rifle/brass that I am working.

Cheers!!

Ole Silver

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Old May 29th, 2012, 08:15 AM   #29
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Ole Silver,

I've read through this thread at least twice (skipping over some of the stuff that, as you mentioned, is more/less not dealing with your original question). I apologize if I've missed it, but I don't feel like you've explained exactly how you originally determined the "bump back" that you use when full-length sizing for your M14.

You said:

Quote:
Originally Posted by Ole Silver
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 assume you mean that you fire form for your bolt gun. But did you ever use a method of fire forming and then gauging off the fire formed case for your M14? If so, what steps did you use exactly?

I apologize; not trying to rub anyone the wrong way. I just feel like after many lengthy posts, the most important question never got asked (or I'm just dense and I missed it) - How much are you bumping the shoulder back upon full-length sizing?

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Old May 29th, 2012, 10:07 AM   #30
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Size your cases to around 0.004" under your rifle chamber headspace and you should be good. After firing your brass should come out all roughly the same cartridge headspace length. I found that measuring before and after firing and comparing the two cleared up a lot of mystery about headspace. The wild card in the M1A / M14 world is the effect of the forcefull ejection on the case, every rifle is different and will subject each ejected case to it's own version of torture.

John

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