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Old February 10, 2013, 12:25 PM   #12
F. Guffey
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Join Date: July 18, 2008
Posts: 2,742
“in fact i recall the unsized (unsized by me but sized by the factory) factory brass from prvi fitting into the chamber fine”

And I said you should have saved one of the unfired cases for reference as in for comparison.

http://www.saami.org/PubResources/CC...%20Swedish.pdf

Note: No mention of head space and case length in the same sentence, head space, as in the length of the chamber from the bolt face to the shoulder/datum applies to chamber length as in ‘measured from’.




“Now the question is - how do i deal with this assuming i only want to push the shoulder back 0.002?”

I have no ideal where the ‘push the shoulder back’ comes from, I suspect it comes from ‘fire formers, chamber a round, pull the trigger, instant gratification, and promotion to the qualification of ‘FIRE FORMER’.

Beyond ‘fire former’ there is ‘case former’ I form cases.

“Okay, not so much an issue as a query. I usually FL size all my rifle cases and bump the shoulder back 0.002. I use a comparator gauge to measure this.

I did the same with my once-fired 7.5x55 swiss brass except the bolt wouldn't close on it.

bumped the shoulder back to 0.004 and the bolt close but required force.

So now i have the die set up to bump the shoulder back a whopping 0.006 and they chamber fine”

I do not know which comparator you are using, in my opinion a bad habit starts with measuring a fired case for case length from the head of the case to the shoulder. Suggestion, before firing measure the new/unfired/minimum length case before firing, I know it is an impossible concept to understand. I measure the length of the chamber from the bolt face to the shoulder/datum first, I also measure the length of the new/unfired case from the head of the case to its shoulder. WHY?I want to know the difference in length between the chamber and case. In the perfect world the difference would be .004” to .006”. Back to some chambers, I have chambers that are longer by .016” than factory/minimum/full length sized cases, (for me?) not a problem, I form cases that are .014” longer from the head of the case to its shoulder, the perfect case for this rifle is the 280 Remington, the case body length is .051” longer than the 30/06 case body. I add .014” to the case length, I raise the die off the shell holder, I am not moving the shoulder back by adjusting the die down .037”, a reloader can not adjust the die down .037”, I raise the die .014”, WHY"? I can measure the distance the die is off the shell holder with anything that measures gaps.

Back to the big inning, you adjusted the die to move the shoulder back, I would have adjusted the die off the shell holder by raising it, to eliminate wild guestimates, I would use a feeler gage, I would adjust the die off the shell holder with a gap of .005”, if after sizing the case I could use the comparator or I could simple attempt chambering the sized case and attempt to close the bolt. If after sizing the case I found the bolt had resistance to closing I would decrease the gap by lowering .002” the die to reduce the gap, again, I would use a feeler gage to verify the adjustment. Then attempt chambering the sized case. If the case chambers without resistance to bolt closing I would know .005” was not enough and .002” would cut down on all that case travel.

Of what you are tying to accomplish is move the shoulder back? Start from the other end, start by adjusting the die off the shell holder, again (impossible concept) it is possible to adjust the die off the shell holder.

Again, I am a case former, move back is a term with an understanding know only to reloaders, I form cases, when I form cases the case shoulder does not move, it is erased, on my 30 Gibbs cases the shoulder becomes part of the case body and the part of the neck becomes part of the shoulder. To a reloader the shoulder moved .205” (forward) to a case former the shoulder did not move, the shoulder is new. Again, know only to reloaders, when does the shoulder go from bump to being erased as in forming?

When adjusting the die adjust off the shell holder, some choose to make wild guestimates, some choose to bump, I choose to adjust off the shell holder, I know the length of the chamber, I understand the dies ability to size a case back to minimum length before I start. In the big inning I scribed the shoulder/case body juncture, Hatcher? That was before me. I did have a friend that accused me of being wrong because he built some magnificent wildcats on 03 and 03A3 receivers, he had case head separation, I informed him I could have told him it was or was not going to happen, I also informed him I could have fixed ‘the problem? if I had had been at the range when he attempted to form his cases.

F. Guffey
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