Help!? 357sig, OAL, Head Spacing, Case Dimensions, Barrel Measurements?? Help!?

Brian Pfleuger · August 22, 2009, 04:49 PM

Please refer to the picture and data below when answering questions:

Questions/Comments:

1)You can see the drastic difference in the shoulder on the three loaded rounds. Apparently, I am essentially fire-forming the GA ammo.

2)Why do you suppose the GA ammo would be so far out of spec on the shoulder? Is it safe?

3)Why does the case diameter of my loaded round change? Is it safe?

4)The OAL length of the reloaded round is too long, however, it is entirely because of the shape of the bullet being round nose instead of flat. It seems to me like this should be OK since it will not effect the head spacing.... if it feeds reliably. Am I right?

5)The sig head spaces on the case mouth.... supposedly. Being that the cases do not match the barrel measurements, apparently it is NOT head spacing on the case mouth. Or am I missing something?

6)Interestingly enough, all the loaded rounds look exactly the same when chambered and they are completely flush on the barrel. (See Pic #2) Considering that the shoulders, case mouths, and barrel measurements are all different, I don't see how this is true....

7)The measurements are causing me to believe that the round is in fact head spacing on the shoulder, as suggested in this article.

8)The measurements that are of greatest concern to me are in red below.

Tell me what I'm missing here. Please be nice to me if I'm being stupid...

Data below:

Barrel Measurements to case stop: (sorry don't know the actual name, the lip where the case is supposed to head space, I think)

Glock: .7295
Lone Wolf: .730

Left to Right,

Speer Gold Dot, fired,

Case: .858
Shoulder ends: .745
Case Diameter: .4295-.4275

Georgia Arms Canned Heat, fired,

Case: .858
Shoulder ends: .744
Case Diameter: .4275-.426

Georgia Arms Canned Heat, unfired

Case: .870
OAL: 1.139
Shoulder ends: .668
Case Diameter: .423-.4215

Speer Gold Dot, unfired

Case: .861
OAL: 1.1355
Shoulder ends: .683
Case Diameter: .4225-.4225

Speer "dummy" reload, Remington 124gr

Case: .858
Shoulder ends: .7265
OAL: 1.1855
Case Diameter: .4225-.4205

Lyman 49th Edition Data

OAL: 1.140
Case: .865
Shoulder: .715
Case Diameter: .424

SL1 · August 22, 2009, 09:09 PM

Like the article in the link you provided, I agreee that the .357 Sig can successfully headspace on the shoulder and that is the way I load it. I set the shoulder so that the case head is 0.002" below flush with the end of the barrel (to leave a little room for powder residue).

I have intentionally made cases short by about 0.100" and fired primers in them to be sure that there was no "shortening of the shoulder dimension" due to firing pin strike forces, etc. They all fired fine. I don't get any misfires in my P-229, even when using "hard" CCI magnum SP primers.

So, I have concluded that the gunwriters' tales about the shoulder being too small and at to shallow an angle to provide a successful headspace surface is rubish.

SL1

SL1 · August 23, 2009, 06:35 PM

One thing I forgot to deal with in your questions was the headspace measurements you provided. Apparently you are measuring to the wrong place(s?) in your barrel, because you said both your Glock and Lone Wolf barrels have measurements around 0.730 inch. But the 357 Sig case is 0.860 inch or a little more. IF it headspaces on the mouth, it must be on a small "step" in the chamber diameter that is something like 0.870 inch from the position of the breach face when the action is closed. The breach face is normally resting against the flat above the chamber on the back of the barrel when the action is closed. You need to measure from that surface to the step in the chamber.

On the other hand, if the case is headspacig on the shoulder, then it can be shorter than the distance to the "step" and still be held back to the breach face. And, even if the case is too short AND the shoulder is too far back, it still is possible for the extractor lip to hold the case rim well enough to allow the firing pin stike to ignite the primer. In that situation, accuracy is usually not good.

SL1

Brian Pfleuger · August 23, 2009, 07:42 PM

Ah! Yes, my you are correct. Dummy me. I will have to measure again when I get home. I neglected to remember that the case head is not flush with the barrel.

So, that mystery is at least reduced. The case dimensions are still a significant question however.

SL1 · August 24, 2009, 07:39 AM

The factory ammo seems to be all over the place with respect to shoulder dimensions, and I think that is due to the factories using the mouths to headspace.

When you fire a factory cartridge in your gun, it fire-forms the case to YOUR gun's chamber. In the process of forcing the shoulder out as far as your chamber will permit, some of the case neck is often pulled back to the case body, leaving a shorter case. Because the 357 Sig is a pretty high-pressure cartridge, it is also possible that the case will stick to the chamber walls and be stretched so that the case head moves back to the breach face That would make the case longer without making the neck shorter, and could lead to case head separations if allowed to happen with repeated relaodings. But, I have not noticed any of my cases stretching, so I don't know if 357 Sigs really do this. I do watch for it, and it is one of the reasons I use the shoulder for headspace.

With respect to your cases growing in diameter, ALL cases grow in diameter from the mouth to a point just in front of the case web when they are fired. If that is what you are talking about, then it is normal and what your size die is there to restore to unfired dimensions. However, the solid part of the case head typically does NOT expand when a case is fire, EXCEPT SOMETIMES ON THE FIRST FIRING. Somewhere around 40,000 psi, depending on brass hardness and case size, case heads will "crush" a little on the first firing, making the solid head (and primer pocket) diameter a little larger. That crushing also work-hardens the brass, and the diameter will not increase again when the case is refired at the same pressure. I have noticed in my 357 Sig that the case heads on Speer Lawman brass DO expand with their first firing, so I am guessing that brass is softer than some other brands. But, it works fine for reloads, and is not dangerous to reuse.

If this doesn't resolve the remaining mysteries, please ask again. And, if those mysteries include the case diameter, please be more specific about where you are taking the diameter measurement. Two common areas are (1) the "pressure ring" which is the largest diameter on the cae body, usually a little in front of the case web, and (2) the case head, over the solid part of the web, just in front of the extractor groove. You can measure the pressure ring with a regular micrometer, but the case rim will typically interfere with the micrometer anvils if you try to use a regular micrometer to measure the case head. You can use a blade micrometer for measuring the case head or you can CAREFULLY file-down the rim at 180°-apart locations to clear the anvils of a regular micrometer. I say "carefully" because you are looking for a few ten-thoudandths of an inch change from the unfired to the fired condition. A slight brush with the file in the area you will measure can spoil that measurement, becasue it will make an irregularity that will cause variations in you measurements with very minor differences in the anvil placement. You need to take the measurements on individual cases both before and after and look for a difference.

If you are measuring the pressure rings, then even a good dial caliper can be used, but a micrometer is still a better choice if you want to try to estimate pressure from the measurements. (From looking at your numbers, I think you are using a caliper and estimating half-thousandths.) Try measuring the pressure ring diameter at multipe points around your case circumference. You will probably see a significant variation on each case. And, the amout of variation will cahnge from case-to-case. That is due to variations in the case wall thickness and the springyness of the brass within a single case. In order to have meaningful measurements, you need to make them in a manner that you can repeat on a single case and get the same number each time. I have found that I can only repeat measurements to one ten-thousandth of an inch if I take a series of measurements around the circumference of a case and look for the maximum and minimum values. Those are repeatable, but any single diameter measurement depends on where on that case circumference I happened to take it.

Measeuring case heads is even trickier, because (1) you are looking for much smaller changes in dimensions, and (2) you are NOT looking for the maximum dimension along the length of the case (as you do with pressure-rings). Case heads typically come from the factory with a little taper towards the case mouth and may end-up with a little taper towards the case head after their first firing. Since you are looking for a CHANGE in diameter caused by the firing, you need to first make sure that you are measuring the same distance from the extractor groove both times (as well as the same points on the circumference). That is hard to do. A little difference in the distance from the extractor can make a few ten-thousandths difference in the diameter measurement. IF that is what you want to measure, then ask here for some tips on how to make repeatable measurements. I won't just type them out here, because this post is already plenty long.

I decided to take the time to write all this out because I think that measuring the effects of firing on your brass is a good thing to do when working-up loads or evaluating a new gun. It can be confusing to start, and can cause a lot of head-scratching, even among the "experts." But, it is a good way to develop an awareness of how things are going BEFORE there are case problems like loose primer pockets or head separations. So, I encourage you to persist. Just be careful if you start trying to use case measurements to esimate peak pressures. There has been a lot written about that, some of which creates a false sense of accuracy because it does not take into account the case-to-case variations in a proper manner.

SL1

Brian Pfleuger · August 24, 2009, 10:40 AM

Quote:

The factory ammo seems to be all over the place with respect to shoulder dimensions, and I think that is due to the factories using the mouths to headspace.

I agree that that the factory rounds are head spacing on the mouth. I am still surprised by the relatively huge variance in factory case dimensions. I have never seen such a thing before. My main experience with factory ammo has always been with rifles cartridges and I have never seen two rounds of the same cartridge that were visibly different.

I am glad to see that my dies are creating a case that is nearly identical to the fire formed cases.

Quote:

if those mysteries include the case diameter, please be more specific about where you are taking the diameter measurement. Two common areas are (1) the "pressure ring" which is the largest diameter on the cae body, usually a little in front of the case web, and (2) the case head, over the solid part of the web, just in front of the extractor groove.

Yes indeedy, sorry, I have never needed to know these terms before.

The measurements are taken at, I guess, the "web" (the first part of the main body after the extraction groove?) and at the top of the main body, just before the shoulder begins to taper.

Basically, the Speer cases varies by no more than about .002 over the entire length and my reloaded case tapers pretty steadily, with a total of .02 top to bottom.
I know that the difference between .02 and .002 is pretty insignificant in normal terms but it seems like a lot for something that can blow my hand apart. It is, after all, 10 times as much taper.

August 23, 2009, 06:35 PM	#3
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	Peetzakilla, One thing I forgot to deal with in your questions was the headspace measurements you provided. Apparently you are measuring to the wrong place(s?) in your barrel, because you said both your Glock and Lone Wolf barrels have measurements around 0.730 inch. But the 357 Sig case is 0.860 inch or a little more. IF it headspaces on the mouth, it must be on a small "step" in the chamber diameter that is something like 0.870 inch from the position of the breach face when the action is closed. The breach face is normally resting against the flat above the chamber on the back of the barrel when the action is closed. You need to measure from that surface to the step in the chamber. On the other hand, if the case is headspacig on the shoulder, then it can be shorter than the distance to the "step" and still be held back to the breach face. And, even if the case is too short AND the shoulder is too far back, it still is possible for the extractor lip to hold the case rim well enough to allow the firing pin stike to ignite the primer. In that situation, accuracy is usually not good. SL1 Last edited by SL1; August 24, 2009 at 07:43 AM. Reason: changed headspace measurement to 0.870" from 0.875" after looking at my notes

August 23, 2009, 07:42 PM	#4
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	Ah! Yes, my you are correct. Dummy me. I will have to measure again when I get home. I neglected to remember that the case head is not flush with the barrel. So, that mystery is at least reduced. The case dimensions are still a significant question however. __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

August 24, 2009, 07:39 AM	#5
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	I'm not sure what mysteries remain. The factory ammo seems to be all over the place with respect to shoulder dimensions, and I think that is due to the factories using the mouths to headspace. When you fire a factory cartridge in your gun, it fire-forms the case to YOUR gun's chamber. In the process of forcing the shoulder out as far as your chamber will permit, some of the case neck is often pulled back to the case body, leaving a shorter case. Because the 357 Sig is a pretty high-pressure cartridge, it is also possible that the case will stick to the chamber walls and be stretched so that the case head moves back to the breach face That would make the case longer without making the neck shorter, and could lead to case head separations if allowed to happen with repeated relaodings. But, I have not noticed any of my cases stretching, so I don't know if 357 Sigs really do this. I do watch for it, and it is one of the reasons I use the shoulder for headspace. With respect to your cases growing in diameter, ALL cases grow in diameter from the mouth to a point just in front of the case web when they are fired. If that is what you are talking about, then it is normal and what your size die is there to restore to unfired dimensions. However, the solid part of the case head typically does NOT expand when a case is fire, EXCEPT SOMETIMES ON THE FIRST FIRING. Somewhere around 40,000 psi, depending on brass hardness and case size, case heads will "crush" a little on the first firing, making the solid head (and primer pocket) diameter a little larger. That crushing also work-hardens the brass, and the diameter will not increase again when the case is refired at the same pressure. I have noticed in my 357 Sig that the case heads on Speer Lawman brass DO expand with their first firing, so I am guessing that brass is softer than some other brands. But, it works fine for reloads, and is not dangerous to reuse. If this doesn't resolve the remaining mysteries, please ask again. And, if those mysteries include the case diameter, please be more specific about where you are taking the diameter measurement. Two common areas are (1) the "pressure ring" which is the largest diameter on the cae body, usually a little in front of the case web, and (2) the case head, over the solid part of the web, just in front of the extractor groove. You can measure the pressure ring with a regular micrometer, but the case rim will typically interfere with the micrometer anvils if you try to use a regular micrometer to measure the case head. You can use a blade micrometer for measuring the case head or you can CAREFULLY file-down the rim at 180°-apart locations to clear the anvils of a regular micrometer. I say "carefully" because you are looking for a few ten-thoudandths of an inch change from the unfired to the fired condition. A slight brush with the file in the area you will measure can spoil that measurement, becasue it will make an irregularity that will cause variations in you measurements with very minor differences in the anvil placement. You need to take the measurements on individual cases both before and after and look for a difference. If you are measuring the pressure rings, then even a good dial caliper can be used, but a micrometer is still a better choice if you want to try to estimate pressure from the measurements. (From looking at your numbers, I think you are using a caliper and estimating half-thousandths.) Try measuring the pressure ring diameter at multipe points around your case circumference. You will probably see a significant variation on each case. And, the amout of variation will cahnge from case-to-case. That is due to variations in the case wall thickness and the springyness of the brass within a single case. In order to have meaningful measurements, you need to make them in a manner that you can repeat on a single case and get the same number each time. I have found that I can only repeat measurements to one ten-thousandth of an inch if I take a series of measurements around the circumference of a case and look for the maximum and minimum values. Those are repeatable, but any single diameter measurement depends on where on that case circumference I happened to take it. Measeuring case heads is even trickier, because (1) you are looking for much smaller changes in dimensions, and (2) you are NOT looking for the maximum dimension along the length of the case (as you do with pressure-rings). Case heads typically come from the factory with a little taper towards the case mouth and may end-up with a little taper towards the case head after their first firing. Since you are looking for a CHANGE in diameter caused by the firing, you need to first make sure that you are measuring the same distance from the extractor groove both times (as well as the same points on the circumference). That is hard to do. A little difference in the distance from the extractor can make a few ten-thousandths difference in the diameter measurement. IF that is what you want to measure, then ask here for some tips on how to make repeatable measurements. I won't just type them out here, because this post is already plenty long. I decided to take the time to write all this out because I think that measuring the effects of firing on your brass is a good thing to do when working-up loads or evaluating a new gun. It can be confusing to start, and can cause a lot of head-scratching, even among the "experts." But, it is a good way to develop an awareness of how things are going BEFORE there are case problems like loose primer pockets or head separations. So, I encourage you to persist. Just be careful if you start trying to use case measurements to esimate peak pressures. There has been a lot written about that, some of which creates a false sense of accuracy because it does not take into account the case-to-case variations in a proper manner. SL1

August 22, 2009, 09:09 PM	#2
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	Like the article in the link you provided, I agreee that the .357 Sig can successfully headspace on the shoulder and that is the way I load it. I set the shoulder so that the case head is 0.002" below flush with the end of the barrel (to leave a little room for powder residue). I have intentionally made cases short by about 0.100" and fired primers in them to be sure that there was no "shortening of the shoulder dimension" due to firing pin strike forces, etc. They all fired fine. I don't get any misfires in my P-229, even when using "hard" CCI magnum SP primers. So, I have concluded that the gunwriters' tales about the shoulder being too small and at to shallow an angle to provide a successful headspace surface is rubish. SL1