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Expanded case head
- Thread starter josh.rizzo
- Start date
mikecr said:Yeah, there is no reason to think there is a primer problem at all.
That was my thought too...which is why I started this thread. It seems to me like there is no way a bad primer caused the kind of expansion to the case head that I'm seeing. But I changed primers and the problem went away, so what am I left with?
Bad brass would possibly make sense. If the webbing was somehow malformed (maybe had a bubble in it?) then it could have expanded improperly, and may have even caused the primer blow-outs. Though I find it hard to believe I would get 20/100 bad cases in a batch of Lapua brass, I guess its possible. And even then, the new primers fixed the issue...but I guess I could have just made it through all the bad cases by then.
I weigh each of my charges by hand with a trickler (not a thrower) on a digital scale and seat the bullet immediately after charging each individual case. I calibrate the scale each time I load a batch and I have confirmed with test weights that its accuracy is +/-0.002 grains. With this powder and bullet I tested that I get a "crunch" (compressed load) at about 41.5 grains, so I know I couldn't have overcharged it by much even if I screwed up royally. My finalized load with the CCI primers is 40.8 grains and there are no pressure signs on that brass or primer. I even played with seating depth on that load from touching the lands to about 0.04" off the lands with no pressure signs on anything.
My first round of testing was at 35 degrees Fahrenheit (ambient temp) and the later round (with CCI primers) was at about 45 degrees. I have an IR thermometer that I use to varify the barrel, chamber, and ammo temp, and never fired anything at more than 5 degrees above ambient.
One thing I thought of is that after the first round of load testing, I pulled about a dozen loaded rounds. They were the hotter loads that I did not fire when I noticed pressure signs on lower loads. I pulled them using a kinetic/impact puller from Frankford Arsenal, and reloaded them with lower charges when fine tuning the load. Could bullet pulling have damaged the cases somehow?
Oh well...I have my load and I'm changing primers and ordering another batch of brass so hopefully I don't see this again. Just wondering what the hell could have caused that kind of expansion on the strongest part of the brass. Thanks for all the responses everyone!
I've read that cold temps can boost pressures but it sounds like they weren't that cold at 35°F. (Not sure of the temp to avoid. I know they say to keep rifle rounds in pocket if hunting in real cold weather.)
But that is the main difference I see, if the brass was same mfgr/lot on good/bad cases.
But that is the main difference I see, if the brass was same mfgr/lot on good/bad cases.
Lapua brass, less capacity, reduce powder charge is what i read online. The loaded rounds neck diameter should not be larger than .3435" Larger and the neck gets crimped into the chamber. Should not be a problem with a factory chamber. Maybe check the web thickness, like here http://www.ar15.com/mobile/topic.html?b=6&f=42&t=276154 Checking the case weight may also tell you something, if there is a large variation. Try a new shell holder from a different company. Last, what does the expanded case head measure? There has been problems with Win. primers leaking, but not making high pressure. http://s338.photobucket.com/user/joe1944usa/library/Firearms%20%20and%20%20Reloading/Primer%20Gas%20Leak Sorry if you already know this.
If you have 3 new UN fired cases measure the base and 1/2 '' up from the base . then take 3 fired and do the same. next take a fired case and full length re size it. the factor case should be smaller then the re sized. The fired case shouldn't be over .002 bigger. If it is you could have a big chamber. The fired case should expand to the chamber size and spring back. If the size 1/2 above is right. Then you may have soft brass or high pressure. Larry
Actually the OP never answer this question and perhaps he does not know the answer which is not unreasonable as although I keep my brass together so that I know how many times I reloaded them, they are all in a single box so looking back at the OP’s post I see that he really has two problems:jlow said:So are all the cases that had over expanded case head came from the Win primer equipped rounds and none of the CCI primer equipped rounds had any problem?josh.rizzo said:Shynloco said:...BTW, did you consider just trying a different brand of primers and see what the result was with the same procedures used with the Win LR primers? Just a thought.
Yes, I switched to CCI #200 primers; everything else was exactly the same except it was about 5 degrees warmer outside on the second day. I it up to 41 grains before even the slightest pressure signs this time. No blown primers or problems of any kind with the CCI stuff.
1) He is getting blown primers with the Win primers which went away after changing to CCI.
2) He is getting 1/5 of his brass stretched out now unusable.
Well the two can but does not have to be related unless OP knows the blown primer brass is the stretched out brass. OP says for the Berger he is shooting, the recommended load for IMR 4320 is 37 gr min and 39.5 gr max but then he tells us he got up to 41 gr of the stuff. I know he said that speed is only 2500 fps but perhaps his chrono is off. If the chrono is off and he is 1.5 gr over max, maybe this is what is causing the brass to stretch out?
jlow said:Actually the OP never answer this question and perhaps he does not know the answer which is not unreasonable as although I keep my brass together so that I know how many times I reloaded them, they are all in a single box so looking back at the OP’s post I see that he really has two problems:
1) He is getting blown primers with the Win primers which went away after changing to CCI.
2) He is getting 1/5 of his brass stretched out now unusable.
Well the two can but does not have to be related unless OP knows the blown primer brass is the stretched out brass. OP says for the Berger he is shooting, the recommended load for IMR 4320 is 37 gr min and 39.5 gr max but then he tells us he got up to 41 gr of the stuff. I know he said that speed is only 2500 fps but perhaps his chrono is off. If the chrono is off and he is 1.5 gr over max, maybe this is what is causing the brass to stretch out?
Trying to cover all this quickly before I leave work, so excuse the shortness of my replies...
This is the first firing of all of this brass. The stretched cases were only on the cases with the WLR primers.
I checked my chrono against a known speed round each time (if you can tell from previous replies, I get pretty OCD about checking my equipment these days). The first session I started by chronoing Winchester Match ammo with the 168gr SMKs, which hit exactly 2800fps +/- 5fps (thats some good ammo, btw). The second session with the CCI primers I checked against my .223REM loads which I know chrono at ~2850fps. Chrono measured known rounds as expected both times. Now its possible my chrono has ALWYAS been off, but that seems unlikely as my calculated drop data is consistent with all measured speeds.
Also, the blown primers (and consequently stretched brass) happened with loads around 38 grains clocking at around 2300fps, so although my final load was 40.8, the primer issues happened well before that in load testing.
Thanks!
OK, that helps a lot. So blown primers and stretch cases were all from the same lot with Win primers. So if the chrono data is correct, then primers were not blown by over powder charging but by over pressure but yet you don’t see significant MV. So there are really only a few things that can cause this, which would include:
1) Jamming into the lands.
2) Too long necks causing bullet crimping.
3) Wet or lubed cases that prevents the cases gripping the walls and excessive bolt thrust.
4) Over sized bullets.
5) Carbon build up in the throat/carbon ring.
If you are right and that is changing primers makes it go away then all of the above can be dismissed… so it comes back to the primers. In this case, not because of flaws in the primer cup but perhaps too hot a primer? Here is a table from German Salazar’s Riflemansjournal that shows how different primers on the same reloading setup has pressure ranging from 57,100 to 61,700.
http://riflemansjournal.blogspot.com/2009/06/primers-large-rifle-primer-study.html
Who knows, maybe those primers were over charged? But here is the thing, if the primers were over charged and caused increases in chamber pressure, why no increase in MV. The only thing I can think of is the primer changed the ignition curve of the powder causing an early spike like a fast burning pistol powder.
1) Jamming into the lands.
2) Too long necks causing bullet crimping.
3) Wet or lubed cases that prevents the cases gripping the walls and excessive bolt thrust.
4) Over sized bullets.
5) Carbon build up in the throat/carbon ring.
If you are right and that is changing primers makes it go away then all of the above can be dismissed… so it comes back to the primers. In this case, not because of flaws in the primer cup but perhaps too hot a primer? Here is a table from German Salazar’s Riflemansjournal that shows how different primers on the same reloading setup has pressure ranging from 57,100 to 61,700.
http://riflemansjournal.blogspot.com/2009/06/primers-large-rifle-primer-study.html
Who knows, maybe those primers were over charged? But here is the thing, if the primers were over charged and caused increases in chamber pressure, why no increase in MV. The only thing I can think of is the primer changed the ignition curve of the powder causing an early spike like a fast burning pistol powder.
Shynloco
You can lead a horse to water, but ........
Guys,
After reading all the posts and ideas of what is the potential cause of Josh's problem, I'm not certain we can get a consensus or actual solution to it. My initial feelings were that "pressure" has to be heightened for the brass to be expanding as described. My point is that there have been several valid potential causes described by several folks and the culprit may be any one of them up to and including everything that's been mentioned or a combination thereof. Still, I hate mysteries.
After reading all the posts and ideas of what is the potential cause of Josh's problem, I'm not certain we can get a consensus or actual solution to it. My initial feelings were that "pressure" has to be heightened for the brass to be expanding as described. My point is that there have been several valid potential causes described by several folks and the culprit may be any one of them up to and including everything that's been mentioned or a combination thereof. Still, I hate mysteries.
I feel the same way till we know how big the chamber is. We are just guessing LarryShynloco said:Guys,
After reading all the posts and ideas of what is the potential cause of Josh's problem, I'm not certain we can get a consensus or actual solution to it. My initial feelings were that "pressure" has to be heightened for the brass to be expanding as described. My point is that there have been several valid potential causes described by several folks and the culprit may be any one of them up to and including everything that's been mentioned or a combination thereof. Still, I hate mysteries.
You are absolutely right of course. Without first hand access to the material, the best that can be done is to theorize. Only the OP has the ability to figure this out.Shynloco said:Guys,
After reading all the posts and ideas of what is the potential cause of Josh's problem, I'm not certain we can get a consensus or actual solution to it. My initial feelings were that "pressure" has to be heightened for the brass to be expanding as described. My point is that there have been several valid potential causes described by several folks and the culprit may be any one of them up to and including everything that's been mentioned or a combination thereof. Still, I hate mysteries.
High Pressure at Starting Load- Primers make a difference
From http://www.shootingtimes.com/2011/01/04/ammunition_st_mamotaip_200909/We tested loads at both maximum normal pressures and at the starting loads (some labs calculate start loads—we shot them). Standard primers caused no ignition issues at the max load but posted higher extreme variations in pressure and velocity in the lower pressure regimes of the start loads. In extreme cases, the start loads produced short delayed firings—probably in the range of 20 to 40 milliseconds but detectible to an experienced ballistician. Switching that propellant to a Magnum primer smoothed out the performance across the useful range of charge weights and completely eliminated the delays.
Reporting back from home with some measurements:
The normal cases I have are 0.405" +/- 0.0005" diameter around the inner ring of the web (the thinnest part, where it wasn't fitting the shell holder.)
Busted cases are 0.410" in the same place, give or take a thousandth. So not as much expansion as I thought, but still enough to keep them from fitting in the shell holders. They still chamber and extract fine though...so could it be the bolt has tolerances that are too loose? Also, I should report that the expanded cases all have pretty distinct extractor marks on them, reinforcing the idea that this was a pressure issue.
The normal cases I have are 0.405" +/- 0.0005" diameter around the inner ring of the web (the thinnest part, where it wasn't fitting the shell holder.)
Busted cases are 0.410" in the same place, give or take a thousandth. So not as much expansion as I thought, but still enough to keep them from fitting in the shell holders. They still chamber and extract fine though...so could it be the bolt has tolerances that are too loose? Also, I should report that the expanded cases all have pretty distinct extractor marks on them, reinforcing the idea that this was a pressure issue.
Other dimensions seem unimpacted. The case head and the base of the case body are at 0.470"-0.471" on all cases. Case thickness around the neck is 0.015"-0.016" on all cases.
Case head thickness is also a constant 0.050" across the board.
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