Anybody still measure case head expansion as a way of seeing pressures?
I have came to the conclusion that its not worth it. I think the only way it can be done is to measure a "new" case before and after firing and seeing the change.
I use a set of starrett mics.
I did a test this weekend, where I was building up a load for my STW. I took the load up in 0.5increments until I felt heavy bolt lift. The cases were new winchester cases. For the most part, I seen 0.0005" case head expansion with the "heavy bolt lift" cases. With the others, for the most part, I seen only 0.0003" or less. So I feel the theory is sound. But several cases did not coorelate the mic measurements and pressure signs.
It's probably a legitimate method. I don't use it because I only have a digital caliper that isn't precise enough to measure ten thousandths accurately. I look for the typical early pressure signs, harder than normal bolt lift and flattened primers. If I see either, I'll back down to the most accurate load below that that didn't show pressure signs.
I have a set of starrett anvil mics. Plus blade mitotoyos calibers. I don't really trust the calibers down to .0001. So only place to measure with the starretts is the rim itself. Or the belt.
Here's my thing. I bet it depends alot on brass brand too. In other words, if you had a pressure strain gauge. And lets say for both pieces of brass, you are reaching 70KPSI. But the webbing of brass A is stiffer. Brass B might show greater than .0005" expansion.
Ken Waters sure did like that method BC. What little I have reloaded I have measured it a little too. My calipers really arent good enough to do it seriously.
Your right about the brass, In my 6.5 I've used win, rem, and nosler brass. with my hunting loads, and believe me noone asks more of a rifle than I do. win will take them in stride, for 5 full power firings, rem. will last 3, noslers lose the pocket the first firing. I do not measure casehead expansion, I go by the "feel" of seating primers.
I shoot lapua brass in my 7mm AM and have shot rounds in warm weather with temp sensative mil-surp powders that were so over pressure that I could not raise the bolt till the rifle was put in an air conditioned truck and allowed to cool and haven't lost a pocket yet. This is why I try to build rifles that I can make brass from lapua cases.
In july of 2007, Tom Sarver set the all time record at 1K BR at Thunder Valley range in Ohio, he shot a 5X/50 that measured 4" and change with a 300 hulk that was formed using 338 lapua cases, those 5 cases on that group were on they're 58th firing.
RR
Mike,
I was told by a tech at sierra once, that if you use fed. 215 primers, they have a soft cup, if a flattened primer is not accompanied by at least one other sign of pressure, (ejector marks, heavy bolt lift, etc) you probably weren't over pressure just approaching max. My 6.5 shows no signs of pressure till the pocket goes, It blows primers and still shows no ejector marks, heavy bolt lift, and all that. it craters primers a bit, but if they're flattened any at all, the pocket is gone.
RR
Thats what I was kinda thinking. Just heading into "shooting" season and was playing around a bit. 58th load? Thats just crazy. Surprised he didn't get a cracked neck at least. But his thoat is probably so tight it probably doesn't work it at all.
That sucks. I bought a bunch of this brass in .308 and .30-06. Oh well. You're not the only one I've heard this from. There are at least two others that have told me Nosler Custom brass isn't all that great.
Tom
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I have come to understand that I really enjoy learning things the hard way.
Case Head Expansion
