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Old February 1, 2013, 11:10 AM   #6
F. Guffey
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Join Date: July 18, 2008
Posts: 2,748
“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”

Bump? I never heard the turn ‘bump the shoulder back...” until I read ‘the forums’, I have instructions that go back to the fifties, bump had nothing to do with the shoulder and everything to do with adjustment.

Davery25, get a good start, as I have said before, “practice does not make perfect”, try this, measure the case length from the head of the case to the shoulder/datum first with new ammo, new ammo is minimum length, if the new ammo chambers save one round for reference when reloading. After firing, measure the length of the case (again) from the head of the case to its shoulder/datum, then compare the difference between the fired/new/minimum length case to the length of the fired case to determine the effect the chamber had on the case when fired.

I do not know where you got the .004” bump? back shoulder setting? I do not know how you determined you were adjusting the die for a .004 adjustment. I start with .000, I accomplish a .000 adjustment by simply adjusting the die down to the shell holder with an additional 1/4 turn of the die, after adjusting the die for full length sizing to minimum length I size a case, then determine if the die, shell holder and press sized the case or if the case had more resistance to sizing than the presses ability to overcome the resistance. Meaning: A reloader can measure the gap between the top of the shell holder and bottom of the die, before lowering the ram, to determine if the press won or the case won. no gap, the press won, a gap, the case won.

Comparator, measure the length of the case from the head of the case to its shoulder before firing, measure again after firing, measure again after sizing. Bump and backwards. You are using a comparator to determine the effect sizing is having on the case, I start with determining the length of the chamber from the bolt face to the shoulder of the chamber/datum. My opinion, you do not have a .000 reference, I full length size to restore a case to minimum length by adjusting the die down to the shell holder with a 1/4 additional turn, I have no ideal what a reloader means when the say they adjust for .00X bump, I use the avoidance system/method, I avoid full length sizing for minimum length by adjusting my die off the shell holder with a feeler gage, the companion to the press because a feeler gage is a standard and a transfer and a means of verifying an adjustment.

Back to your question, you are bumping the shoulder back .006”? You started with .004” My opinion, you should have started with .000 by adjusting the die down to the shell holder, then to determine if the case was restored to new factory loaded length you should have compared the case with your new, never fired case. If the case chambered without resistance I would suggest you back the die out a 1/4 turn then try again. eventually you will get to the point where you started, eventual you will get to the point where a case will not chamber without resistance to bolt closing. I am the fan of cutting down on all that case travel.

There is something about the tapered sides of a round case forming cone...etc., ...etc.. One day? Then there is the diameter of the chamber, who knows? I do, but I make no excuses, I am a case former. Not starting at .000, you do not know the length of the chamber, you assume you have fire formed the case to fit the chamber from the from the bolt face to the shoulder of the chamber, again, I am not a fire former, I form first then fire, because I start with a reference of .000. I can do little with the effect the chamber has on the case body except neck size, when fired the case fills the chamber, when the chamber body allows the case body to expand the case increases in diameter, it happens, back to the tapper and cone, when the reolader insist on restoring the case to minim length/full length and takes liberties with something they do not understand (as in bump) they do not take into consideration reducing the diameter of the case increases the length of the case from the head of the case to the shoulder/datum. I start with .000, backing the die out and of off the shell holder allows the reloader to have control over the length of the case and diameter of the case body.

Then there is the part about using the comparator without knowing where you are headed, by accident you are adjusting the die to overcome resistance to sizing, all under the heading of ‘BUMP’. Bump? sounds like an accident, there is nothing I do that resembles an accident, I know, if I incorporated bump it would sound like I was going for neighbor acceptance.

“Does anyone know why the shoulders need to be bumped back so much in the k-31?” You first, explain how you determined you you were shortening the case length from the head of the case to its shoulder .004” then to .006”. Remember, full length sizing to minimum length is .000, again, I adjust the sizer die off the shell holder .014” when sizing cases for one 30/06 chamber. This method works well for the length of the chamber from the bolt face to the chamber shoulder and does the same for the tapered cone of the chamber. Starting at .000 the .014” is a plus when added to the length of the case from the head of the case to the to its shoulder, travel as in case travel? .002”

F. Guffey

Last edited by F. Guffey; February 1, 2013 at 11:18 AM. Reason: change an O to an I
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