Case dimension change.

02 March 2016, 23:16

FYI
Ran a mini experiment on case dimension change on once fired Lc 74 .308 cases before and after Full Length sizing.
Base diameter before = .4705" . After .468"
The change in case length varied .003" to .004" LONGER.

Who knows maybe this will be helpfull to someone some day?

roger

03 March 2016, 03:14

wildcat junkie

quote:
Originally posted by bartsche:
FYI
Ran a mini experiment on case dimension change on once fired Lc 74 .308 cases before and after Full Length sizing.
Base diameter before = .4705" . After .468"
The change in case length varied .003" to .004" LONGER.
Who knows maybe this will be helpfull to someone some day? roger

The brass has to go somewhere when it is squeezed back to the smaller size. That's why we trim case length after a few cycles..

By the same token, when fire forming Ackley Improved cases, the OAL of the parent case shrinks by as much as .012" or more if I remember correctly.

03 March 2016, 08:14

bartsche

10-4 WJ- Another contributer is draging the case out of the die over the expander and some times when tight getting slight elongation.

roger

03 March 2016, 13:43

Andre Mertens

If, after FL sizing, you measure the depth of the primer pocket, you will notice that it is shallower and has lost some depth. When cold worked, brass does indeed expand in all directions, front and rear. Therefore, to restore the primer pockets dimensions and depth, I routinely clean them out with a pocket uniformer and it shaves a little every time.

03 March 2016, 15:30

jeffeosso

roger --
the resizer is making it longer .. take the expander out and retry.. you'll get the same results

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03 March 2016, 22:12

bartsche

quote:
Originally posted by jeffeosso:
roger --
the resizer is making it longer .. take the expander out and retry.. you'll get the same results

I was thinkinking of doing just that.

03 March 2016, 22:28

bartsche

Did three more cases from the same lot. with the expander removed. The stretch was as much as .007". Resized the same three with the expander in the die. Little if any change in lenth.

This small sample does not prove ,however, that a tight neck does not cause case elongation.Variables such as thick necks or hardend brass do tend to lengthen the cases and to the point that the shoulders move out and prevents chambering. Through the years I have wittnessed this.

Also checked to see if the primer caused the difference in measurements. The primers did not change the measurements.

roger

05 March 2016, 07:39

wildcat junkie

quote:
Originally posted by bartsche:
Did three more cases from the same lot. with the expander removed. The stretch was as much as .007". Resized the same three with the expander in the die. Little if any change in lenth.
This small sample does not prove ,however, that a tight neck does not cause case elongation.Variables such as thick necks or hardend brass do tend to lengthen the cases and to the point that the shoulders move out and prevents chambering. Through the years I have wittnessed this.
Also checked to see if the primer caused the difference in measurements. The primers did not change the measurements. roger

The case "stretched" when it was fired albeit in diameter, not length. When you squeezed the diameter back to original, the brass had nowhere to go but forward, thus elongating the case. It wasn't "stretched" by the resize, it was pushed.

05 March 2016, 20:45

bartsche

quote:
Originally posted by wildcat junkie:
[QUOTE]Originally posted by bartsche:

The case "stretched" when it was fired albeit in diameter, not length. When you squeezed the diameter back to original, the brass had nowhere to go but forward, thus elongating the case. It wasn't "stretched" by the resize, it was pushed.

I guess I could have been more explicit and used better terminology but it seems you got the picture.

roger

19 March 2016, 00:20

Atkinson

The whole case changes to fit a particular chamber as chamber vari as reamers get used and wear, so no chamber is the exact same..Hot loads add to the delima in that we measure pressure by head expansion, and case length, thus we resize and trim cases..You can play with the expander ball and get some relief there, and also file it down some and get a tighter grip on the bullets, and even that will increase pressure by perhaps one or two PSI's..