Shoulder Bumping Inconsistencies

[71firebird400]

I'm trying to wrap my head around this one;

Fired Lapua brass (338LM)
Forster FL Die w/ expander ball installed
Redding Competition Shellholders
Lee Lube

Measured fired cases and they were all +.005"; gauge was zero'd out using virgin brass. Took two cases and started with the .010" shellholder, had to use the .008" shellholder before I saw a .002" shoulder bump. Proceeded to run the remaining cases through the die with the .008" shellholder and got the following;

1 case showed zero bump (+.005" headspace)
4 cases showed .001" bump (+.004" headspace)
13 cases showed .002" bump (+.003" headspace)
2 cases showed .003" bump (+.002" headspace)

Lube was installed uniformly, on the case neck, case body, and inside the neck - no lube on the shoulder. Press operation is also very consistent. I remeasured the cases a couple times and the numbers were repeatable. I then took the 5 cases that were not showing enough of a shoulder bump and ran them through the press again; headspace remained unchanged from the initial measurement.

Any ideas?

 

[turbo54]

Re: Shoulder Bumping Inconsistencies

Is your die set so that you are camming over the press?

I've found similar inconsistencies when I DON'T cam over.

 

[71firebird400]

Re: Shoulder Bumping Inconsistencies

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">Is your die set so that you are camming over the press?

I've found similar inconsistencies when I DON'T cam over. </div></div>

Die is setup so it won't cam over. I suppose that could be an issue with consistency? Good catch.

 

[DHDeal]

Re: Shoulder Bumping Inconsistencies

I agree on the camming over of the press keeping my cases at a consistent "bump". I now have my dies and shell holders matched together, for a lack of a better way to put it. I have found that I can get all of my sizing dies to cam over in my press. It is an OLD Lyman Orange Crusher and I have considered many times to replace it, but I do not want to go through resetting everything.

 

[RTH1800]

Re: Shoulder Bumping Inconsistencies

Also might consider a bushing die. Your expander ball pulling back through the neck could be tugging the shoulder a bit.

 

[Suasponte]

Re: Shoulder Bumping Inconsistencies

I have found that fast stroking your press in and out of your sizing die affects headspace the most. Slow down your press stroke and let the brass normalize in the die. Every case has a different spring back rate even brass out of the same lot number.

Also, get rid of the expander as it too will affect the headspace when pulling it back thru the neck.

As long as your consistent with your press stroke over camming only puts stress on your press that is not needed to acheive your goal. Once the shell holder contacts the bottom of the sizing die you have got all you can get out of the die.

Terry