| Case stretch - how much? [message #15897] |
Sun, 11 November 2012 08:38  |
wallypedal
Messages: 13
Registered: November 2012
Location: Wyoming
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Long time Encore guy, first time poster! I have a 7-08 barrel that gave me fits for a long time, but I've finally got it settled down. While experiencing the Encore learning curve I had a couple of early partial case separations. That forced me to learn the whole headspace/dial indicator/barrel-frame gap/sizer setting/internal case inspection routine. Very interesting to me.
I have now figured for myself that I will determine my personal 'max' loads by the amount of case stretch experienced when firing loads which are sized to .001" - .002" less protrusion than the barrel to frame gap. Right now, I don't want loads that stretch more than .004" total - or cases which stick out .002" MORE than barrel to frame gap after firing. Hope that description makes sense. BTW, I do all this measuring with the extractor removed, using the MB dial indicator rig.
The question: What do you folks who measure and tinker like I do handle this? How much stretch do you have, what do you find acceptable, how long do cases last depending on stretch, etc? I read one poster who says he experiences NO stretch and can neck size only. Those would be wimpy loads in my barrels.
Wallypedal
[Updated on: Sun, 11 November 2012 08:39] Report message to a moderator |
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| Re: Case stretch - how much? [message #15917 is a reply to message #15902] |
Sun, 11 November 2012 16:05  |
wallypedal
Messages: 13
Registered: November 2012
Location: Wyoming
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Forum Newbie |
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Jim,
Yep case separation is bad for sure. That's why I said I experienced them early in the process with this barrel. They were due to excess resizing in combination with what were excess loads for this barrel. The good part was the separation problem forced me into learning the rest of the protocol for sizing and measuring properly. I think I got it, and the barrel shoots well now.
Here's what you said, "Your "acceptance" of .004 case stretch means that you have at least .002 "barrel"/frame gap (actually barrel/bushing), PLUS another .002 in the chamber (hence the backing off sizing die suggestion being likely needed)."
That's not the situation. I have cases that are sized consistently to .0015" less than barrel/bushing gap, so that the action is putting no pressure on the loaded case when closing. The actual protrusion of the case changes after firing to .0025" MORE than barrel/bushing gap, giving the .004" stretch I'm speaking of. The .004" is made up of the .0015" the case stretches to strike the bushing, plus the accumulated stretch from the frame,hinge pin, locking lugs and locking table variables which all add up and always amount to something when firing full power loads.
Believe me, I've read and re-read all that MB says on this subject, and am confident I've got it understood. I don't have excess headspace, nor the sizing die screwed down too far. Otherwise, I would not be able to size cases to that .0015" less than barrel to bushing gap. Firing pin bushing shims would only force me to screw the sizing die in MORE in order to achieve
the resized case clearance described.
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From Mike B: "With the extractor removed, you can measure how far fired cases are protruding from the frame at various pressure levels. The more force there is on the frame, up to a point, the more the cases will stick out of the barrel when fired. You may find that cases that stick out of the barrel, say, .003" more after fired than before shoot better than those that stick out, say, .005." Monitoring this can be valuable information in determining "sweet spots" where a barrel shoots best."
************
So that is what my question was about: "For folks who do the dial indicator measuring of case protrusion before and after firing, what have you found that is an acceptable amount of stretch in relation to accuracy and case life?" For me and this barrel, it ended up being .004". I can tell you that .008" is too dang much!!
I appreciate your interest and response. This stuff is hard to verbalize and visualize, and I'm sure I confused the question with TMI.
Tom
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| Re: Case stretch - how much? [message #17436 is a reply to message #15897] |
Wed, 26 December 2012 15:52 |
jingles
Messages: 17
Registered: December 2012
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Forum Newbie |
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I have been experiencing case stretch in my 308. I have bellm shim kit comming and as I understand it when using the resizing die one should try and leave the case as long as possible. I am trimming the cases as per reloading tables for max lenght. I assume this must be done as the length is on the neck. I guess my questionn is how do you take the extractor out. Do you have to drive the little roll pin out and if so is that a big deal?
Thanks
Tim
telecaster
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