Char-Gar
04-07-2013, 04:17 PM
I know nothing, zero, zip, nada about metals in general and cartridge brass in particular, but I have noticed something that puzzles me and I am certain some of you have the answer.
Cartridge brass seems to "springback" when expanded and not so when compressed. To be specific, I am talking about the case necks of 30-06 cases. I have been doing some fiddling and measuring and this is what I have found;
1. Measure the neck expanding plug and then the ID of the case that has been passed over it and there will be about .001 "springback". i.e. a case passed over a .310 expander will have a .309 ID. Use a .311 expander and the ID will be .310.... I have done this with expanders from .307 to .314 and each time the expanded case measures .001 less than the expander. We are talking +- .0002 here and I am certain this number will vary with make of brass and how many times it has been sized. In this instance, they were once fired R-P cases.
2. Measure the diameter of the neck area in a FL sizing die and then the OD of a case ran through it and there is less than .0002 if any difference. I am using a Lyman Shell Resizer hand die in an arbor press. I repeated this with an older C-H FL size die and got the same results.
So, expand a case neck and it "springsback". Compress a case neck and it stays put. Why is this?
Please don't give me a lecture on how to use precision measuring tools as I know how and these numbers are correct. I used good Starrett Small Hole Gages and a good Starrett 1" micrometer that reads out to .0001. I have 50 plus years of experience in their use
If you know the answer, please don't use "tech talk", terms and concepts I would not understand. If I knew those terms, I probably wouldn't need to ask this question.
Cartridge brass seems to "springback" when expanded and not so when compressed. To be specific, I am talking about the case necks of 30-06 cases. I have been doing some fiddling and measuring and this is what I have found;
1. Measure the neck expanding plug and then the ID of the case that has been passed over it and there will be about .001 "springback". i.e. a case passed over a .310 expander will have a .309 ID. Use a .311 expander and the ID will be .310.... I have done this with expanders from .307 to .314 and each time the expanded case measures .001 less than the expander. We are talking +- .0002 here and I am certain this number will vary with make of brass and how many times it has been sized. In this instance, they were once fired R-P cases.
2. Measure the diameter of the neck area in a FL sizing die and then the OD of a case ran through it and there is less than .0002 if any difference. I am using a Lyman Shell Resizer hand die in an arbor press. I repeated this with an older C-H FL size die and got the same results.
So, expand a case neck and it "springsback". Compress a case neck and it stays put. Why is this?
Please don't give me a lecture on how to use precision measuring tools as I know how and these numbers are correct. I used good Starrett Small Hole Gages and a good Starrett 1" micrometer that reads out to .0001. I have 50 plus years of experience in their use
If you know the answer, please don't use "tech talk", terms and concepts I would not understand. If I knew those terms, I probably wouldn't need to ask this question.