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Bumping Shoulders Issue

 
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  #1  
Old 03-13-2010, 02:54 PM
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Bumping Shoulders Issue

Hello All,

On the advice of many here I decided to give bumping a try as opposed to simply neck sizing. To say that my first attempt did not go well is an understatement. I'm hoping that by describing what occurred that someone can offer me advice.

Here goes. I first took the fire formed brass and I measured it using the RCBS precision mic. The measures varied somewhat but I settled on .002 larger than Sammi. I chose to bump the shoulder .002 so that would essentially mean that I need to bump the shoulder into Saami spec. Zero on the gauge.

I then put the brass in the press and sent the ram to the top. Then I started to thread the FL sizer die down onto the cartridge until it stopped. At this point the die is sticking out of the press like 1/2 - 5/8". This is from a normal position where I would FL size when business as usual. I lowered the ram and dialed the die down a half turn. Lubed the case and sent it up into the die. It met very little resistance pulled it out and miced it. The measure didn't change. Turned the die down a little more, send in the brass, mic again. No change. Did this a couple more times. Nothing. Sent another fire formed brass into the die and it came out .004 under saami spec. Dialed the die out a bit and tried it again. Nothing.

I went through several pieces of brass trying this before giving up and deciding to write a post here. I had a buddy with me and he was as confused as I was.

Any ideas what I did wrong?

Back up inf0: remington brass, Lee dies, Lyman press

Thanks

Tom
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  #2  
Old 03-13-2010, 02:56 PM
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Re: Bumping Shoulders Issue

Also wanted to add. I put the die in as instructed. Meaning hit the shell holder and then 1/4 turn more. This yeilded similar results as above. Wild changes in head space based on small movements of the die. Not always in the same direction.

Thanks in advance to anyone that can assist.

Tom
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  #3  
Old 03-13-2010, 05:00 PM
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Location: Sonoma County, CA
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Re: Bumping Shoulders Issue

Are you depriming before taking any measurements? Primers can be at different heights and will give you varying measurements.
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Old 03-13-2010, 05:20 PM
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Re: Bumping Shoulders Issue

Not sure I can solve anything for you here but I can share what I do.

I drill two holes in two sides of a hex nut. One hole is slightly larger than the fired case neck. This allows me to get a datum on the case shoulder for reference as I size the case. In my gun it turns out my brass only grows .002" at the shoulder when fired. I have to use the entire length of my FL sizer to bump the shoulder back. I find I get better accuracy FL sizing than neck sizing in this gun.

A second smaller hole that rests on the bullet ogive and I use it as the datum point when seating bullets. Again, it's a relative measurement, but once established it's easy to get a seating depth for bullets of similar ogive design.
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Old 03-13-2010, 05:23 PM
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Re: Bumping Shoulders Issue

Statjunk, I'll try and explain in a little better detail.

First, I would deprime your cases. Then take your measurements from case head to the datum line using your pm. You should start to see more consistent readings. When setting up your die, back it off a little for starters, remember the threads are course and a little goes a long way. When I am setting up dies, I leave the lock ring lose and backed off so I can turn the die in very small increments, measuring each time. You may only turn the die an 1/8 turn or so to get into the right area, and then just a very slight bump/turn while fine tuning it. As you are adjusting it, you may even see your shoulders grow as the case is being resized and brass flows into the shoulder, in this case just screw it down a bit more. You want to fine tune the position of the die to only bump the shoulder back a small amount. Don't worry too much about where the bottom of the die is in relationship to your shell holder.
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Old 03-13-2010, 05:35 PM
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Re: Bumping Shoulders Issue

You only bump the shoulder when you need to bump the shoulder or you do it based upon a knowledge of your chamber.

Here is what to do (and there are probably easier methods but this is mine)

Take your fired brass and start running it through your rifle until you find one that makes the bolt hard to close. Perhaps find a couple more just to double check things being as this is your first time.

Go to your press and screw in the sizing die but leave it about a quarter inch or so high.
Lube the brass inside and out
Run the brass through the die and then try it in the chamber. It will probably still be stiff

Go back to the die and screw it down some more being as you didn't bump the shoulder. Run the piece of brass through and check it in the rifle again.

Keep doing this until you finally get the die screwed in to just barely size the case enough that the bolt closes easily.

At this point you need to do two things.

Get your runout gauge out and check the neck for straightness. If it is straight then lock the ring on the die so that it will never ever move again. If the neck is not straight then you have to fiddle with the lock ring and try to get the die lined up to where it is straight and then lock down the ring tight so it never ever move again.

To sum it up, I do not use a measuring tool. I use the feel of the bolt closing to determine when the die is set properly to "bump the shoulder"
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  #7  
Old 03-13-2010, 06:30 PM
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Re: Bumping Shoulders Issue

Realize that an 1/8th turn of the die represents 0.009" of height. If you make fine adjustments using a feeler gauge between the die and the shell holder, you will find it easier to get to where you want to be.
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