Inconsistent Shoulder BlowOut on Fired Cases - ???

[Phil3]

I am shooting an AR-15 and have shot factory ammo from PMC and Blackhills, as well as stuff with a WCC headstamp, and my own reloads using Winchester cases. I would have thought all would measure pretty close from shoulder to case head. Not the case. They vary over .005". How can I properly set die shoulder setback when the fire formed cases dimensions are all over the map? I've checked and rechecked and they just aren't consistent. I could see maybe my own starting loads my have been too light to blow out the cases, but factory ammo?

I tried Bigedp51's approach of determining actual headspace. That process involves fitting a spent primer into a new case so it sticks out of the case maybe half way. Then slowly chamber the round, remove, and measure from primer surface to shoulder. I chambered the case as slowly as possible and the bolt had the ejector removed. Extractor stayed in so I could get the case out. I don't think any of my fired cases measure as long as the test case.

To me, the chamber has to be at LEAST as long as the test case, unless inertia forced the primer further into the case. I kinda doubt that. Does it make sense then to set back the shoulder on my die based on test case dimensions or set back even further from where the fired cases are now? If I set back based on the shorter fired cases by .004", and the chamber is as long as the test case shows, the headspace is going to be like .009"!

Phil

 

[BigDMT]

Is your BCG lubed well and operating without sticking? Should be able to throw the bolt face forward pretty easily while holding on to it in your hand.

If the BCG is sticking somehow one time, then not the next, I could see how maybe brass shoulders could change by ejecting at different levels of gas pressure on the BCG. By that I mean one case ejects sooner than the next and does not fully form to the chamber before being ejected. Just a thought, I may be way off...

 

[bigedp51]

There is still pressure in the barrel as the AR bolt moves to the rear (over gassed) and this pressure can move the shoulder forward. In simple English a fired case can end up longer than the chamber, because the bolt is gas operated and not stationary.

Full length resize a case making hard contact with the shell holder (cam over) "THEN" use the spent primer trick to find your head clearance or the "air space" between the rear of the case and the bolt face.

Don't worry about how long your fired cases are, worry about how long your chamber actually is.

Using the primer method, your primer protrusion is equal to your shoulder bump and you adjust the die until you have .002 to .004 head clearance.





This very old method dates back to 147 BG (before gauges) and should not be confused with "BC" (before cartridges) and was also used as the cheap bastards adjustable headspace gauge.

 

[bozo699]

There is still pressure in the barrel as the AR bolt moves to the rear (over gassed) and this pressure can move the shoulded forward. In simple English a fired case can end up longer than the chamber.

Full length resize a case making hard contact with the shell holder (cam over) "THEN" use the spent primer trick to find your head clearance or the "air space" between the rear of the case and the bolt face.

Don't worry about how long your fired cases are, worry about how long your chamber actually is.

Using the primer method, your primer protrusion is equal to your shoulder bump and you adjust the die until you have .002 to .004 head clearance.

Sooooo Big Ed what is your thoughts on lubing the cases? bwahahahaha!!!!!
Wayne.

 

[bigedp51]

Sooooo Big Ed what is your thoughts on lubing the cases? bwahahahaha!!!!!
Wayne.

I would love to hate you Wayne but I can't..................................

Your "almost" as funny as I am......... bazinga!!!!!

 

[bigedp51]

Phil3

Read the link below and "over gassed" will have more meaning. Just by changing bullet weight or type powders can effect fired case length in a gas operated rifle.

Case-Head Swipe
http://www.shootingillustrated.com/index.php/8720/case-head-swipe/

 

[bozo699]

Sooooo Big Ed what is your thoughts on lubing the cases? bwahahahaha!!!!!
Wayne.

I would love to hate you Wayne but I can't..................................

Your "almost" as funny as I am......... bazinga!!!!!

Ditto I don't shoot ar's but very useful info Ed.
Wayne.

 

[BigDMT]

Very useful info. But I believe his dilemma is centered around the fact that he is getting very inconsistent headspacing from fired cases. Over .005" difference. Not just short head spacing, and not just long head spacing. It's both.

Ed, because he has only been using factory ammo with these results, do you think that a good consistent hand load could cure this? Perhaps it could if his rifle is sensitive to the inconsistent pressure/velocities often found with factory ammo.

I know BCG's can be pretty sticky on new rifles, so I'd check that to be sure.

Then find the actual head spacing of your chamber with the primer method outlined by Ed, sort your fired brass to within .002" tolerance of safe head spacing and only use those pieces for initial hand load testing. Load those cases carefully with accurate charges of powder and fire them again to see if the sorted brass with known tight head space tolerances is coming out with varying head spacing as with the first firing when brass was factory ammunition. If it is, then you may have a gas pressure issue as Ed suggests. Then you'll just have to find out what is causing it. If the brass comes out within the same tolerances, then you will know it was due to the inconsistency of the factory loaded ammo.

Let us know how it turns out. Good Luck!

 

[243winxb]

 

[jhord]

I don't know if this will help, but I've been firing some IMI surplus ammo in my RRA NM for practice and to get a new batch of brass for match ammo. Out of the can the surplus ammo has about .006" headspace. After firing it only lengthens about .003". After the next firing it will blow out all the way and need set back. If you are firing a mish-mash of factory and reloaded ammo, you are going to get a mish-mish of shoulder measurements. (the way it was sized at the factory, the quality and thickness of the brass, the rifle setup, etc etc) Take your measurement from some cases that have been fired a few times and that should give you the "true" headspace dimension, and base your shoulder bump on that. AR's can be tricky to reload for if you are trying to "minimally size" the brass.

 

[bigedp51]

I am shooting an AR-15 and have shot factory ammo from PMC and Blackhills, as well as stuff with a WCC headstamp, and my own reloads using Winchester cases. I would have thought all would measure pretty close from shoulder to case head. Not the case. They vary over .005". How can I properly set die shoulder setback when the fire formed cases dimensions are all over the map?
Phil

Very useful info. But I believe his dilemma is centered around the fact that he is getting very inconsistent headspacing from fired cases. Over .005" difference. Not just short head spacing, and not just long head spacing. It's both.

BigDMT

You are correct, he has at least four different types of cartridge cases, four types of brass that vary in hardness, and four different pressure loadings.

I went through the same thing as the OP, I have three five gallon buckets of .223/5.56 range brass fired by our local SWAT Teams and police departments on the same day. It is Remington, Federal and Lake City brass fired in countless different AR15 rifles.

1. The OP needs to know the actual chamber headspace length of his AR15.

2. The OP needs to sort his brass and stick with one type/brand.

3. I full length resized all of my cases with the die making hard contact with the shell holder and started from scratch.

NOTE: I'm loading for three different AR15s and a bolt action .223, and I also spent a good deal of time scratching my head with the same problem multiplied severial times.

Bottom line, get the longest cases at least .002 to .004 shorter than actual chamber headspace length and forget the short cases, they will grow.

Also measure new .223/5.56 unfired ammunition, I found they run .005 to .006 shorter than the GO gauge.

In closing I will leave you with the very funny words of wisdom from a shooting buddy of German A. Salazar written at "The Rifleman's Journal"

"I get the best accuracy when my cases fit the chamber like a rat turd in a violin case"

 

[CatShooter]

I am shooting an AR-15 and have shot factory ammo from PMC and Blackhills, as well as stuff with a WCC headstamp, and my own reloads using Winchester cases. I would have thought all would measure pretty close from shoulder to case head. Not the case. They vary over .005". How can I properly set die shoulder setback when the fire formed cases dimensions are all over the map? I've checked and rechecked and they just aren't consistent. I could see maybe my own starting loads my have been too light to blow out the cases, but factory ammo?

I tried Bigedp51's approach of determining actual headspace. That process involves fitting a spent primer into a new case so it sticks out of the case maybe half way. Then slowly chamber the round, remove, and measure from primer surface to shoulder. I chambered the case as slowly as possible and the bolt had the ejector removed. Extractor stayed in so I could get the case out. I don't think any of my fired cases measure as long as the test case.

To me, the chamber has to be at LEAST as long as the test case, unless inertia forced the primer further into the case. I kinda doubt that. Does it make sense then to set back the shoulder on my die based on test case dimensions or set back even further from where the fired cases are now? If I set back based on the shorter fired cases by .004", and the chamber is as long as the test case shows, the headspace is going to be like .009"!

Phil

I've loaded approximately 18 tons of 223 ammo for ARs in the past few years, and I think you are being anal about it.

ARs are not precision benchrest rifles (regardless of what AR owners tell you ) they are machine guns that are missing a few trigger parts.

There is no need to "bump" shoulders back 3 or 4 thou, cuz you will never get the cases to fully fit the chamber in the first place - it is not the nature of the animal.

There two types of case sizing problems that affect ARs - the first is long headspace - the bolt lugs lock part way closed because the case is too long - these clear the rifle easily.

The second is a body jam that is caused by the body diameter not being sized - these are a real pain to clear.

To set your die, do it the old fashioned way of screwing down a FL die (preferably a SB FL die), til it hits the shell holder, and back it off 1/4 of a turn, and size the case.

Then try chambering a case by hand. If the body wants to stick, bring the die down 1/30-ish of a turn, size a different case, and try it.

Keep doing it until the die body does not stick, and then give the die another 1/30th of a turn.

If the shoulder is OK for headspace and the bolt closes without any resistance, then lock the die setting and enjoy it.

If, for some reason, the shoulder is causing the bolt not to close all the way, then continue bringing the die down in 1/30ths of a turn until the cases function smoothly. You will never be able to control case dimensions in an AR the same way as you can with a quality bolt gun.

 

[BigDMT]

I am shooting an AR-15 and have shot factory ammo from PMC and Blackhills, as well as stuff with a WCC headstamp, and my own reloads using Winchester cases. I would have thought all would measure pretty close from shoulder to case head. Not the case. They vary over .005". How can I properly set die shoulder setback when the fire formed cases dimensions are all over the map?
Phil

Very useful info. But I believe his dilemma is centered around the fact that he is getting very inconsistent headspacing from fired cases. Over .005" difference. Not just short head spacing, and not just long head spacing. It's both.

BigDMT

You are correct, he has at least four different types of cartridge cases, four types of brass that vary in hardness, and four different pressure loadings.

I went through the same thing as the OP, I have three five gallon buckets of .223/5.56 range brass fired by our local SWAT Teams and police departments on the same day. It is Remington, Federal and Lake City brass fired in countless different AR15 rifles.

1. The OP needs to know the actual chamber headspace length of his AR15.

2. The OP needs to sort his brass and stick with one type/brand.

3. I full length resized all of my cases with the die making hard contact with the shell holder and started from scratch.

NOTE: I'm loading for three different AR15s and a bolt action .223, and I also spent a good deal of time scratching my head with the same problem multiplied severial times.

Bottom line, get the longest cases at least .002 to .004 shorter than actual chamber headspace length and forget the short cases, they will grow.

Also measure new .223/5.56 unfired ammunition, I found they run .005 to .006 shorter than the GO gauge.

In closing I will leave you with the very funny words of wisdom from a shooting buddy of German A. Salazar written at "The Rifleman's Journal"

"I get the best accuracy when my cases fit the chamber like a rat turd in a violin case"

LOL! Have never heard that one, but I like it

You are right. I kinda overlooked the fact that he is measuring many different types of brass. That's probably exactly the problem.

 

[Phil3]

There is still pressure in the barrel as the AR bolt moves to the rear (over gassed) and this pressure can move the shoulder forward. In simple English a fired case can end up longer than the chamber, because the bolt is gas operated and not stationary.

MY OP says I did not think any of the cases were as long as the chamber. Cases may end up longer than the chamber, but that is NOT my problem here.

Full length resize a case making hard contact with the shell holder (cam over) "THEN" use the spent primer trick to find your head clearance or the "air space" between the rear of the case and the bolt face.

I used a new case, as it notably shorter than just about any fired case. I could resize as you said, but I would end up with a case with dimensions similar to a new case.

Don't worry about how long your fired cases are, worry about how long your chamber actually is.

I know. As my OP says, I did measure the chamber, using your method. With my tools, that dimension is 1.4325" Others have mentioned that different brand cases could result in varying lengths after firing and there is some truth to that.

Blackhills 223 Remington Match: Fired cases range from 1.4285 to 1.4305. That is .003" variance.
PMC Bronze: 1.4295 - 1.4305: That is .001" variance.

I did not measure other brands of brass. As a side note, the PMC ammo was always more accurate than the Blackhills...

The above results do indicate that fired brass length is influenced by brass brand. Good to know.

Using the primer method, your primer protrusion is equal to your shoulder bump and you adjust the die until you have .002 to .004 head clearance.

 

[Phil3]

Phil3

Read the link below and "over gassed" will have more meaning. Just by changing bullet weight or type powders can effect fired case length in a gas operated rifle.

Case-Head Swipe
http://www.shootingillustrated.com/index.php/8720/case-head-swipe/

There is no indication of over gassing, except with some Blackhills 223 Remington 55 FMJ ammo that was using 5.56 NATO cases. With that, I did have some case head swiping. But, that has not been seen on any other cases, either from factory ammo or hand loads.

Phil

 

[Phil3]

Very useful info. But I believe his dilemma is centered around the fact that he is getting very inconsistent headspacing from fired cases. Over .005" difference. Not just short head spacing, and not just long head spacing. It's both.

Based on the chamber length measurement I took (did twice), ALL fired cases are shorter than the chamber. How much shorter is what varies.

Ed, because he has only been using factory ammo with these results, do you think that a good consistent hand load could cure this? Perhaps it could if his rifle is sensitive to the inconsistent pressure/velocities often found with factory ammo.

I am still working up loads, and do not have a consistent hand load to try. Those early handloads were light, and very well could be responsible for some cases that measured notably shorter than the chamber. Just not enough pressure to really blow the shoulder forward.

I know BCG's can be pretty sticky on new rifles, so I'd check that to be sure.

The rifle was built by me and has at least 500+ rounds through it.

Then find the actual head spacing of your chamber with the primer method outlined by Ed, sort your fired brass to within .002" tolerance of safe head spacing and only use those pieces for initial hand load testing. Load those cases carefully with accurate charges of powder and fire them again to see if the sorted brass with known tight head space tolerances is coming out with varying head spacing as with the first firing when brass was factory ammunition. If it is, then you may have a gas pressure issue as Ed suggests. Then you'll just have to find out what is causing it. If the brass comes out within the same tolerances, then you will know it was due to the inconsistency of the factory loaded ammo.

Understood, and can do that.

Phil

 

[Phil3]

1. The OP needs to know the actual chamber headspace length of his AR15.

I have done this using bigedp51's method, twice.

2. The OP needs to sort his brass and stick with one type/brand.

Yes, I can now see the importance of that.

3. I full length resized all of my cases with the die making hard contact with the shell holder and started from scratch.

I will adjust the die to set back the shoulders about .004" from what I know to be the chamber length. Maybe a tad more to guarantee no stuck cases.

NOTE: I'm loading for three different AR15s and a bolt action .223, and I also spent a good deal of time scratching my head with the same problem multiplied severial times.

Bottom line, get the longest cases at least .002 to .004 shorter than actual chamber headspace length and forget the short cases, they will grow.

Understood. Many cases are already a few thou shorter than the chamber length, so they won't need much shoulder setback.

Also measure new .223/5.56 unfired ammunition, I found they run .005 to .006 shorter than the GO gauge.

In closing I will leave you with the very funny words of wisdom from a shooting buddy of German A. Salazar written at "The Rifleman's Journal"

 

[Phil3]

I've loaded approximately 18 tons of 223 ammo for ARs in the past few years, and I think you are being anal about it.

No. I am trying to learn, be safe, understand my rifle, and achieve best accuracy and reliability.

ARs are not precision benchrest rifles (regardless of what AR owners tell you ) they are machine guns that are missing a few trigger parts.

I know what they are, just trying to make mine shoot as accurately as possible.

There is no need to "bump" shoulders back 3 or 4 thou, cuz you will never get the cases to fully fit the chamber in the first place - it is not the nature of the animal

There two types of case sizing problems that affect ARs - the first is long headspace - the bolt lugs lock part way closed because the case is too long - these clear the rifle easily.

You completely lost me here. No need to set the shoulders back? Shoulder setback is what controls headspace, but you then say long headspace can be a problem with the AR. ???

The second is a body jam that is caused by the body diameter not being sized - these are a real pain to clear.

To set your die, do it the old fashioned way of screwing down a FL die (preferably a SB FL die), til it hits the shell holder, and back it off 1/4 of a turn, and size the case.

Then try chambering a case by hand. If the body wants to stick, bring the die down 1/30-ish of a turn, size a different case, and try it.

Keep doing it until the die body does not stick, and then give the die another 1/30th of a turn.

If the shoulder is OK for headspace and the bolt closes without any resistance, then lock the die setting and enjoy it.

If, for some reason, the shoulder is causing the bolt not to close all the way, then continue bringing the die down in 1/30ths of a turn until the cases function smoothly. You will never be able to control case dimensions in an AR the same way as you can with a quality bolt gun.

This process assumes that when I test chamber a case, I can somehow tell the difference between a case that won't chamber because of a swollen body and one that has insufficient head space (shoulder setback). How is that done?

Phil

 

[bigedp51]

This process assumes that when I test chamber a case, I can somehow tell the difference between a case that won't chamber because of a swollen body and one that has insufficient head space (shoulder setback). How is that done?

Phil

I know the topic of 223 Remington vs 5.56 has been discussed endlessly, but just wanted to remind AR owners they should be absolutely certain of what chambering they have before loading it up with 223 or 5.56 military.

I built my AR and ordered a barrel from Krieger. I told them I would be shooting 223 only and wanted the absolute best accuracy. Krieger used a specific reamer to achieve that and as I recall, was instructed never use 5.56 ammo. I recently called them and they researched their records and found my barrel serial number. They said that barrel was reamed to minimum 223 Remington SAAMI specs and should absolutely not be used with 5.56 ammo.

Rifles are sold and bought all the time, and I think it wise to be absolutely sure what is safe to fire in it and what is not. 5.56 may not be safe.

Phil

Phil

You already know what type custom chamber you have and I will call it "minimum size", my AR15s have larger military chambers and I will call them "maximum size". The replies you have gotten here may have forgotten your earlier post above and given you "maximum size" military chamber advice.

Some of the commercial cases fired in my "maximum size" chambers will not drop all the way into a Wilson case gauge because the base of the case is too large in diameter. After resizing these same cases would fit in the Wilson gauge and chamber correctly, meaning I did not have a problem with body diameter.

Because you have a minimum sized chamber there will be a chance a "normal size" reloading die will not make the body diameter small enough. Meaning you might need a small base die, BUT first try the standard die for reliable clambering.

Don't beat yourself to death over shoulder bump, my first full length Lee die was bumping the shoulder back .010 shorter than my fired length when camming over in the press. I checked these cases with my RCBS case mastering gauge and found "NO" thinning in the web area after being fired. I later bought a RCBS FL die that bumped the shoulder back .005 less than the Lee die. Meaning the RCBS die resized my cases to the same length as new ammunition and approximately .004 shoulder bump.



Any .223/5.56 brass made to military specs will be harder in the base and be less effected by stretching. "Some" brands of commercial brass may be more prone to stretching in the web due being softer SAAMI spec brass.

Just work on the shoulder bump that works for your rifle 100% and you will be good to go.