Case Head Expansion
12-21-2009, 07:43 AM
#1
Guest
Posts: n/a
Case Head Expansion
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.
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.
12-21-2009, 08:46 AM
#2
Nontypical Buck
Join Date: Feb 2003
Location: Coralville, IA. USA
Posts: 3,802
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.
Mike
Mike
12-21-2009, 10:09 AM
#3
Guest
Posts: n/a
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.
Just thinking outloud.
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.
Just thinking outloud.
12-22-2009, 04:49 AM
#6
Nontypical Buck
Join Date: Aug 2004
Location: Michigan
Posts: 3,329
