Okay, so I know all of the usual pressure indicators like flattened primers, cratered primers, extractor/ejector marks. My question is on something more measurable. IE case head expansion. In particular what do you all that pay attention to this think is to much and where exactly are we talking about measuring this at? On a regular cartridge and on a belted cartridge. I would like to use this along with the visual clues to monitor pressure as I like to have something that can be measured and monitored if that makes sense. Thanks.
Case head expansion
- Thread starter wvuredneck09
- Start date
For me, this is the best way to measure for 'MyMax Load', because a 'pressure problem' for me is head expansion & need for a lot of body sizing. That point means shorter case life, and potential to bugger up easy extraction.
I use a blade mic ~at the webline(~.200" forward of groove).
I fireform culled cases twice, neck sized only, get a baseline measure, and then with loads incrementing upward I watch that baseline hold until it step changes another .0005". That's the point where FL sizing of the body will be required. If I continue upward, very little from there, I'll see interference fit & tough extraction that goes with it. 'MyMax' is the point where FL sizing is required. This is what I log.
Now if I had other indicators along the way that are/could be an actual 'problem', then I'm challenged to fix those problems individually(not load-wise). In other words, my chamber and brass tell me when the load is a problem. I don't let the bolt tell me.
I use a blade mic ~at the webline(~.200" forward of groove).
I fireform culled cases twice, neck sized only, get a baseline measure, and then with loads incrementing upward I watch that baseline hold until it step changes another .0005". That's the point where FL sizing of the body will be required. If I continue upward, very little from there, I'll see interference fit & tough extraction that goes with it. 'MyMax' is the point where FL sizing is required. This is what I log.
Now if I had other indicators along the way that are/could be an actual 'problem', then I'm challenged to fix those problems individually(not load-wise). In other words, my chamber and brass tell me when the load is a problem. I don't let the bolt tell me.
I have a flash hole gage, it only works when I measure the diameter of the flash hole first. Years ago it was decided factory loaded cases expand .00025" at the case head. When developing loads the reloader keep case head expansion to .00025". That worked when the reloader did not have the equipment available to them that is available to day.
I have formed cases for wildcat chambers. Out of 440 magnum belted cases 40 would not fit the #4 RCBS shell holder. The builder of the wildcat rifles thought there must be another shell holder and asked me to bring my 'other shell holder'. I brought a small case friendly ball peen hammer. Rational? The cases fit the #4 shell holder before the cases were sized and before firing. The case expansion in front of the belt was .014", the case head expansion at the extraction groove was .011". I offered to size the case in front of the belt with collets in one of his lathes and I offered to cut the extraction groove, I also suggested he not use the cases.
Point? Someone loaded and fired cases that expanded .011" on one firing. I have fired cases once and had the primer fall out when the case was ejected.
Tools, it has been suggested a bladed micrometer be used, then there is a difference in shell holders and the inside diameter of the die at the base. A case without case head expansion can be inserted into the die with the case head first. If the case head is too large in diameter the case head could be upset or the die could have problems.
F. Guffey
Now i'm even more confused, I've heard the 0.005 thrown around before but wouldn't you want to do it on a neck sized case after only 1 reload? Also I have a RCBS casemaster that i think would give repeatable accurate measurements locking in both the diameter and spot on the case the same every time.
If you are asking me if I would want to start with a neck sized case? No.
If I fired a case once and if that case head expanded .001" during the first firing I would believe I exceeded the cases ability to handle the pressure. .001" is 4 times the amount of case head expansion for factory loaded ammo. .005" ??? I can only see short case life for a case head that expands .005", a case that is fired twice with .005" case head expansion would require a lot of creative sizing.
I could say: Remember. Or look at it this way: When the case head expands it also shortens between the top of the cup above the web to the chase head. When someone considers the case head crushing at the same time the case body is locked to the chamber there is only one thing left to happen, that would be the case head separating from the case body.
F. Guffey
Case head expansion that can be delt with depends on the chamber sizing dies don't size the whole base . The base the brass has enough mass to where it can withstand normal pressures . Most dies can correct the normal expansion area. But when exsive
Pressures over rides the mass area you you can't size with dies the case ends up hangin On removing some chambers you can loose primers and the case will chamber.
I have cases that have ben reloaded 20 plus times still wth tight primer pockets
I also have some that junk after 3 reloads. Powder choice was the problem . That went away when I picked a temature insitisive powder.
I have stub that is chambered and is a the same as a 12 ga shotgun shell . I use it in a shotgun to fire forum brass . It also works great when checking for head expanisation .
Larry
Pressures over rides the mass area you you can't size with dies the case ends up hangin On removing some chambers you can loose primers and the case will chamber.
I have cases that have ben reloaded 20 plus times still wth tight primer pockets
I also have some that junk after 3 reloads. Powder choice was the problem . That went away when I picked a temature insitisive powder.
I have stub that is chambered and is a the same as a 12 ga shotgun shell . I use it in a shotgun to fire forum brass . It also works great when checking for head expanisation .
Larry
Yes i meant 0.0005 sorry about the typo. neat idea on using an old 12 gauge to fireform.
In the beginning the .00025 was a starting point. .0005" would be excessive.
As Savagedasher said the base of the die not size the base of the case. The shell holder with a deck height of .125" prevents that from happening. Then there is the radius at the opening of the die.
Fired 20 times and still going. Case head expansion stops after the case head work hardens. Meaning if a case is fired 10 times the case head no longer increases in diameter after about? the third firing. I had rather my cases head expand than to split open because they were worked hardened. I know, strong case heads are in demand.
F. Guffey
BoydAllen
Gold $$ Contributor
Back in the day, I helped a friend, who is a meticulous reloader, with a project, by coming up with the print dimensions for a tight neck .300 Weatherby that had a freebore length that would allow bullets that were seated so that they would fit in the magazine of the Weatherby MK5 action, and touch the rifiling. Because there was no available load data, we approached load workup quite cautiously, starting in the lower loads of the reloading manual, and working up by half grains. I worked with a single case, neck sizing, firing and loading it at the range, with weighed charges. We used a permanent marker to mark the case across the head so that when we measured the belt diameter (with a .0001 mic.) that the measurement would be more uniform. The brass was Weatherby, which I believe was made by Norma. As we started, the first firing produces some belt expansion, even though the fired case gave no other indication of pressure. After that, until the last test, the belt diameter remained stable. As we got to higher and higher pressure, at some point, a circle appeared that showed that the pressure was high enough to move the brass slightly into the ejector hole. The diameter of that rifle's ejector was on the large side. finally, about a grain and a half over the manual maximum load, the belt diameter increased again, slightly, and we stopped. Generally, I do not find head expansion to be the indicator that I want to use for top pressure, because the brass from different manufacturers can be very different in hardness. I prefer to look at primers, bolt lift feel, and in some cases that bright spot that show up on case heads where the ejector hole is. Generally, over the years, I have become less prone to push the limits, having seen examples of what that can produce. Another thing that I keep track of is primer seating feel. If I start to feel primers seating easier, after only a few firings, I know that I need to retune at lower pressure.
Out of 440 belted magnum cases I found all the belts to be the least of the problems. I did find 40 of the cases would not fit the #4 RCBS shell holder. the diameter of the case head at the extractor groove had expanded .007" thousands and the case ahead of the belt had expanded as much as .014". My opinion the cases took a pounding, I could have used a collet in a lathe to reduce the diameter of the case in front of the belt and I could have cut the extractor groove. to make a point I used a small case friendly ball peen hammer to fit the cases to the shell holder.
F. Guffey
Things to adjust in perspective;
- We're not talking about stretch back to the boltface(separation potentials). That's not what's being measured with a blade mic.
If you want to mitigate separations then it's a simple matter of minding headspace. And ANY body sizing during fireforming negates this test all together.
- This is a local test that's all about the local chamber, brass, powder, etc. Dies and shell holders play no role with it.
- This does not produce a pressure value, as local means just that. It's about finding a pressure problem (prelude to loose pockets/extraction issues). This test is showing you the load where FL sizing will actually be required. If you intend to FL size anyway, like if the cartridge design requires it anyway, then there is no reason to do this test. It won't ever mean anything to cases sized near webs.
Keep in mind that if your chamber clearance near webs is ~5thou, 1st firing will cause yielding of the case to this, and after springback you'll likely be ~1thou under chamber. Next fireforming, on that unsized body, will again follow the expanding chamber and spring back to just a tad under chamber springback(~.0005). You can run with this clearance with no body sizing and a normal load for a few more cycles, and then bolt turn will be too annoying to mess with. Why would it keep growing without going higher in pressure? Because that brass yielded so much to begin(with so much chamber clearance), and yielded brass continues to yield & faster. It doesn't get stronger with all that yielding, it get's weaker.
I wanted to learn about the often declared 'requirement to FL size near webs. So I measured NEW brass, and set a improved chamber reamer .0005 over(fitted). My notion was that brass that never yielded to begin would never do so -until forced to(with extreme pressure).
It turned out I was able to reload the fired cases over 40 times with no body sizing at all, and no extraction issues. The brass is still going just fine. There is a little more to it in that I made sure I had enough barrel steel around the chamber, and I set & verify shoulder bumps at under 1thou. My conclusion is that FL sizing requirements are a matter of choices made rather than certainty.
On this chamber the neck is also fitted and no neck sizing or annealing has ever been needed.
I have to bump because the shoulder angle is 35deg. Next chamber will be at least 45deg(maybe 60deg), as I'm hoping to remove all sizing need. The only way I'll know is to keep experimenting.
I run the blade mic test to find 'MyMax' because I don't intend to FL size, ever, with any of my cartridges. The test very accurately tells me the point I can go up to in load development without crossing that line. It doesn't mean I couldn't go higher still, but I chose not to. The fitted chamber in my experiment is 26wssm Imp(capacity matching 260AI). My accuracy load is 47.4gr IMR4350, providing 3025fps with 139Laps. BAT action. QL puts this at ~65Kpsi, SAAMI max, which some would consider moderate/conservative.
I've taken it to 3150fps, MyMax, but I doubt it would shoot as well up there, and I know this rare brass(today) would not have survived it. Doesn't make sense to do it,, it doesn't make sense to drive 26cal bullets past mine,, so it doesn't make sense to go larger in capacity than 260AI for this cal. Choices..
- We're not talking about stretch back to the boltface(separation potentials). That's not what's being measured with a blade mic.
If you want to mitigate separations then it's a simple matter of minding headspace. And ANY body sizing during fireforming negates this test all together.
- This is a local test that's all about the local chamber, brass, powder, etc. Dies and shell holders play no role with it.
- This does not produce a pressure value, as local means just that. It's about finding a pressure problem (prelude to loose pockets/extraction issues). This test is showing you the load where FL sizing will actually be required. If you intend to FL size anyway, like if the cartridge design requires it anyway, then there is no reason to do this test. It won't ever mean anything to cases sized near webs.
Keep in mind that if your chamber clearance near webs is ~5thou, 1st firing will cause yielding of the case to this, and after springback you'll likely be ~1thou under chamber. Next fireforming, on that unsized body, will again follow the expanding chamber and spring back to just a tad under chamber springback(~.0005). You can run with this clearance with no body sizing and a normal load for a few more cycles, and then bolt turn will be too annoying to mess with. Why would it keep growing without going higher in pressure? Because that brass yielded so much to begin(with so much chamber clearance), and yielded brass continues to yield & faster. It doesn't get stronger with all that yielding, it get's weaker.
I wanted to learn about the often declared 'requirement to FL size near webs. So I measured NEW brass, and set a improved chamber reamer .0005 over(fitted). My notion was that brass that never yielded to begin would never do so -until forced to(with extreme pressure).
It turned out I was able to reload the fired cases over 40 times with no body sizing at all, and no extraction issues. The brass is still going just fine. There is a little more to it in that I made sure I had enough barrel steel around the chamber, and I set & verify shoulder bumps at under 1thou. My conclusion is that FL sizing requirements are a matter of choices made rather than certainty.
On this chamber the neck is also fitted and no neck sizing or annealing has ever been needed.
I have to bump because the shoulder angle is 35deg. Next chamber will be at least 45deg(maybe 60deg), as I'm hoping to remove all sizing need. The only way I'll know is to keep experimenting.
I run the blade mic test to find 'MyMax' because I don't intend to FL size, ever, with any of my cartridges. The test very accurately tells me the point I can go up to in load development without crossing that line. It doesn't mean I couldn't go higher still, but I chose not to. The fitted chamber in my experiment is 26wssm Imp(capacity matching 260AI). My accuracy load is 47.4gr IMR4350, providing 3025fps with 139Laps. BAT action. QL puts this at ~65Kpsi, SAAMI max, which some would consider moderate/conservative.
I've taken it to 3150fps, MyMax, but I doubt it would shoot as well up there, and I know this rare brass(today) would not have survived it. Doesn't make sense to do it,, it doesn't make sense to drive 26cal bullets past mine,, so it doesn't make sense to go larger in capacity than 260AI for this cal. Choices..
Thanks for all of the info so far. 40 reloads on a piece of brass is amazing and talk about a well cut chamber/ your reloading practices.
the case head expansion would be greater. Then there is that part about work hardened cases. Guffey, I think you took the context of quoted from the wrong paragraph.
The difference between the two scenarios is initial clearance.
Cases that continue to grow, have likely yielded in high clearance chambering.
My chamber is fitted, so my cases have never yielded. They follow the chamber and spring right back like new brass -everytime.
I didn't say anything about work hardening, or annealing case heads, but firing doesn't work harden cases. Only cycles of sizing does that.
And with this, once brass yields, all the sizing in the world will never make it what is was beforehand.
Brass changes a little bit with every sizing cycle, and there is no way to exactly undo the changes.
The difference between the two scenarios is initial clearance.
Cases that continue to grow, have likely yielded in high clearance chambering.
My chamber is fitted, so my cases have never yielded. They follow the chamber and spring right back like new brass -everytime.
I didn't say anything about work hardening, or annealing case heads, but firing doesn't work harden cases. Only cycles of sizing does that.
And with this, once brass yields, all the sizing in the world will never make it what is was beforehand.
Brass changes a little bit with every sizing cycle, and there is no way to exactly undo the changes.
These topics of case head expansion can be explained by normal material behavior
1. Stress is the load applied. In a rifle cartridge it is PSI.
2. Strain is the deformation (stretching or compression) of a material.
3. A material such as brass will yield (stretch) in a linear proportion until the proportional limit is reached.
After this limit is reached it will stretch faster with less stress increase until it reaches the elastic limit. Once the elastic limit is reached the brass is permanently yielded and will no come back to its original dimensions.
4. If the chamber is a close fit the brass cannot be stretched to the elastic limit because the metal around the chamber is taking the stress.
5. When you have a case head expand permanently in the area not supported by the chamber you have overloaded that case and the stress caused the case to yield past the elastic limit.
6. My observations are when you have primers that will not retain themselves you have a chance for leaking primers and gas cut bolt faces. i do not understand why any one thinks they could use a .010 expanded primer pocket.
1. Stress is the load applied. In a rifle cartridge it is PSI.
2. Strain is the deformation (stretching or compression) of a material.
3. A material such as brass will yield (stretch) in a linear proportion until the proportional limit is reached.
After this limit is reached it will stretch faster with less stress increase until it reaches the elastic limit. Once the elastic limit is reached the brass is permanently yielded and will no come back to its original dimensions.
4. If the chamber is a close fit the brass cannot be stretched to the elastic limit because the metal around the chamber is taking the stress.
5. When you have a case head expand permanently in the area not supported by the chamber you have overloaded that case and the stress caused the case to yield past the elastic limit.
6. My observations are when you have primers that will not retain themselves you have a chance for leaking primers and gas cut bolt faces. i do not understand why any one thinks they could use a .010 expanded primer pocket.
No one thinks it is possible to seat a primer into a primer pocket that has expanded .010".
The OP was asking about case head expansion, in the beginning it was suggested case head expansion for factory over the counter new ammo expanded .00025". And then there was a little confusion about the case head expanding .005" as in somewhere in the back of the OP mind he was kicking that number around. After looking at it the OP decided the number should have been .0005".
F. Guffey
Thanks for clarifying already for me fguffey. I understand the stress/strain and material properties fine but I guess i should have been more clear. I recently had some 270WSM loads that are getting tough to chamber, these were FL sized for the 4th time (purchased as loaded ammo and reloaded 3 previous times, now being loaded again). I found that the issue with chambering was at the case head due to expansion. Loads are being fired in a factory savage so obviously the chamber is loose enough to allow the stretching. I never monitored this before and plan to in the future though and was looking for advise. Like I said i read somewhere that if you see more than 0.0005 you are over pressured. The load I have been loading for the rifle is not noticeably flattening the primers or any of the other typical over pressure signs I know to look for. No bolt lift/extraction issues either. In addition only some of the cases are chambering difficultly, all have been fired in the same gun with the same load the same number of times. No noticeable signs of head separation either, probed the inside of the cases with a high tech paper clip 
. Cases where annealed at last loading (3rd) after having a few necks crack, Its a friends rifle and he refuses to spend the cash on a good set of dies so overworking in the standard RCBS FL sets is the only option.
. Cases where annealed at last loading (3rd) after having a few necks crack, Its a friends rifle and he refuses to spend the cash on a good set of dies so overworking in the standard RCBS FL sets is the only option.BoydAllen
Gold $$ Contributor
The first thing that I would do is measure a fired case, and compare its dimensions with those of a sized one. If the die is set properly, to bump the shoulder the correct amount, and is dimensioned properly, relative to the chamber, then sized brass, that has been trimmed to the appropriate length, should chamber with normal effort. Also, how was the brass annealed?
Fired vs sized cases show 0.002 shoulder bump, cases were trimmed during this last reloading session. Annealing was done on a bench source machine using tempilaq to set it up (650 just below the shoulder not over 800 at the neck, not over 450 at case head. Bullets are seated with 0.015 jump so that isn't an issue. Colored the cases causing an issue with a dry erase marker and forced them to chamber (no tools needed just way to much force for a hunting load) Dry erase marker was gone right around the case head area just above the web. Found that the cases that are difficult to chamber are about 0.004 larger in diameter at this location than the ones that are chambering easily. Primer pockets are far from new but not shot by any stretch either.
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