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Bumping the Shoulder Question

 
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  #1  
Old 11-17-2008, 04:25 PM
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Bumping the Shoulder Question

I had some brand new Norma Brass in a 300 WM and have since fired them once. I will be using a Redding Body Die and a Lee Collett Neck sizer. I was told that I should only bump the shoulder back about .001 to .002. How is this done and do you think that my accuracy will get better since it has been sized to my chamber?
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Old 11-17-2008, 04:48 PM
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Re: Bumping the Shoulder Question

Seeing as the brass has been fired in your chamber, you need some sort of device to measure the length of your brass from the head to the shoulder. I believe that Hornady offers such a tool mounted on a dial caliper. Once you measure you can then set your FL sizing die to only move the shoulders back .001-.002". I can't say that accuracy will benefit but, your brass will last longer. When I chamber a rifle for a customer I always include a small piece of barrel with the neck and shoulder area cut in one end. This widget can be used to measure the amount of bump.
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Old 11-17-2008, 06:40 PM
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Re: Bumping the Shoulder Question

If it's a bolt action, I'd just neck-size it...unless you're having problems chambering the reloaded round. Your brass will last longer since it's fire-formed to your chamber and it should be more accurate. Please correct me if I'm wrong...
Good luck!
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Old 11-17-2008, 09:37 PM
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Re: Bumping the Shoulder Question

Old Heli Logger, With norma Brass, how many firings can I expect to get before it starts to get a bit tight to chamber? I do also have some sort of body die that sizes just above the belt if it starts to get fat. (By the way, it is a bolt action.)
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  #5  
Old 11-17-2008, 11:18 PM
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Re: Bumping the Shoulder Question

Hey samson

Hornady makes a head and shoulders gauge

MidwayUSA - Hornady Lock-N-Load Headspace Gage 5 Bushing Set with Comparator

It clamps onto your caliper and you take measurements close to the datum line on the case




Your case will most likely not expand enough with one firing to get a crush fit in the chamber. On a 300 win mag I own I get the following measurements during the firing cycle:

New case - 2.253" (subtracting the 2" for the gauge and the measurement itself is not important, only it's relationship to the other measurements)
Once fired - 2.270"
Twice fired - 2.272" (slight crush fit)
3 times fired - 2.2725" (crush fit and time to push the shoulder back)

So I neck size only with a Lee Collet for the first 3 firings and then push the shoulder back to 2.272" with a Redding Body Die for a slight crush fit. You will have to push the shoulder back each subsequent firing after.

Note that almost all the expanding happens on the first firing but the case has not been through it's full cycle of expansion. A caveat to this is that if you size the body and not just neck size then when the die squeezes the case body it will push the shoulder forward just a little. IME not enough to make it have a crush fit and it will not be consistant.

When sizing, set your rifle up in a vise and chamber the round as you go through the sizing process and it will tell you when you are developing a crush fit. Until you do, neck sizing will be sufficient.
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Old 11-18-2008, 08:17 AM
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Re: Bumping the Shoulder Question

Woods,
I noticed that when I took an old case that was a crush fit and ran it through the Body Die, It did push the shoulder forward and not set it back. What do I do then?
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Old 11-18-2008, 08:45 AM
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Re: Bumping the Shoulder Question

Thread the die in a little further, resize and try it again in your gun. Keep doing that until you feel the case become easy to chamber. I like a very slight crush fit in my loads.

When adjusting the die move it a very little. I find it advantageous to make marks with a magic marker on the die, lock nut and press



In this photo the difference shown between the marks on the lock nut and die threads can move the shoulder back .002" which is about the amount needed to take a case from a crush fit to no shoulder contact. Sometimes it takes forever when zeroing in on the exact die adjustment and you may have to adjust in bigger turns and go past the point where you push the shoulder back too far and then trash that case, then go back to find the exact point of a slight crush fit.
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