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How to bump the shoulder???

 
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  #1  
Old 11-03-2007, 04:54 PM
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How to bump the shoulder???

I hear alot of guys talking about only neck sizing and bumping the shoulder back... say .002". I am familiar with neck sizing but have always just full length resized when the cases seemed to have a little resistance chambering. I was just wondering if somebody could explain the process of bumping the shoulder back. I was also wondering if it will help with brass life by working the brass less. Thanx guys.

Colin
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  #2  
Old 11-03-2007, 06:03 PM
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Shoulder bumping

If I full length resize, I try to be very careful to bump the shoulder back only a .001 or 2. A friend of mine didn't check & wound up with several separated 223 cases. The problem stopped when he reduced the amount of headspace for the rounds. The old Stoney Point (now Hornady?) or Sinclair int'l tools are great for this job: to custom fit both headspace and bullet depth to a particular rifle.

Forster Products now makes a bushing die to size necks AND bump the shoulder at the same time without touching the case body walls. You might want to look into that. Drop a note or send a ph # if you'd like to discuss more. J
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Old 11-03-2007, 06:10 PM
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When you full length resize you set (bump) the shoulder back. However, it is usually too much. When guys are talking about "bumping he shoulder back 2 thousands", for example, they are using the FL die but not completely resizing the brass.

What a lot of guys do is rezise a minimal amount and chamber the case, resize a little more, chamber, etc until the case just chambers. That is also known as partial FL resizing. The best way to do it is to buy a set of redding competition shellholders which are a 5 shellholder set with each holder being .002 bigger. What you would do is start with the biggest and work your way down until your brass just chambers. Now you know exactly how much shoulder bump you did.

I mentioned that the are using a fl die, however they could be using a body die and neck sizing also.

Also, if you are shooting deer & elk at closer ranges this may not be needed.

YMMV
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Old 11-03-2007, 06:12 PM
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It's really very easy. Using an Overall length gauge (I use the Stoney Point but there are others) measure the base-to-shoulder distance on a once fired case. The tool will measure to a point on the shoulder known as the datum line.

Once you have this measurement you can adjust your FL die down far enough to shorten this length by .001" or .002", as measured on the same gauge. Start with the die backed out a bit and slowly work your way down by sizing-measuring-adjusting (repeat-repeat-repeat) until you get the shoulders to the point that you want.
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Old 11-03-2007, 06:42 PM
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Varmint Hunter is right on, but using the competition shellholders eliminated the need to keep adjusting the die.
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Old 11-03-2007, 07:05 PM
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+1 Varmint Hunter and Roll Ur Own.

Exactly correct. In my loading book for one of my rifles I have written.

"Adjust FL die to touch +10 shellholder, then use +8 shellholder to size .001" under chamber".

I can setup that die in 10 seconds and be perfect the first time using the competition shellholders.


AJ
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Old 11-04-2007, 09:23 AM
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You need to remember that Redding +0.0X" shell holders are not always the answer.

Because all chambers have +/- tolerances, and all sizing dies have +/- tolerances, you can have (and I have had) a situation where the headspace in a die is longer than the headspace of the chamber.

So when the case gets tight to chamber, you cannot "bump" the shoulder, because when you put the case into the die, the shoulder of the case does not touch the shoulder of die, so you cannot set it back.

In this situation, you must modify shell holders to have a "minus 0.0X" length. The standard shell holder has a standing hight of 0.125" +/- 0.001", and these are held to tight tolerances... but you may have to take 10 thou or more off of the top of the shell holder to be able to bump the shoulder back 0.001", if your chamber is shorter than the bump die's headspace.

I have a set of shell holders that are shortened by lapping on a plate with #800 carbide paper. Each one was made for a specific rifle, and specific die, to exactly match the chamber.

I have one shell holder that had to be taken down 0.023", before the die would touch the shoulder of the case.

The point of this is that there are no automatic solutions to the "bump" issue.



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