Shoulder bump

sbindy

sbindy

Steve B
Up until now I have been using two different gauges to measure how much I was bumping the shoulder, and setting it back .001 on the gauge. On the third firing my cases were a little tight when the bolt closed. I checked them after firing and found that I still had .001 bump, but the rounds still chambered hard.
So I took my rifle and put a fired case in the chamber, and measured the force it took to close the bolt with a trigger pull gauge. It read 5lbs. I then checked a sized case and it read 3 1/2lbs. Empty took 2lbs to close it.
I then adjusted my FL die by marking the die and ring, downward slightly until it only took 2lbs to close the bolt. I only had to move it the width of the mark.
There has to be a difference in way that the comparator's measure to the datum line and the actual dimension the case is when it conforms to the chamber such as a slight difference in shoulder angle of the chamber, or in the die when it resizes it. Either way, it doesnt work until the bolt closes without resistance.
The rifle is a Savage action with a Douglas 30BR barrel installed and shoots very well, until the bolt lugs were under tension, then the groups opened up alot.
Just passing this along so that maybe someone else can find it useful:)
 
There is more to sizing a case than just pushing the shoulder back. It sounds like your die is not sizing the case body. On 6mmBR there is an article on the Harrell's sizing dies and in the article is a coarse way to check the sizing of the body.

I have used the Harrells dies on 3 different bbls and have been totally satisfied.
 
sbindy.

What does the shoulder measure now that the bolt closes??? You MUST know that it's the shoulder dimension that's binding or you're likely to have a case head separation.

crb is right.


BTW, if your groups are opening up when the lugs are under tension then you've got some other problems with the rifle. IME rifles which are more accurate with loose brass or while fireforming have got machining alignment issues.

al
 
crb

Im using a Redding Type S FL bushing die, and it sizes all the way down the case. At least as far as a FL die is supposed to anyway. :)
 
alinwa

It now measures .002 shorter than after firing. Being that this is with a factory Savage action, bolt lug misalignment is probably a given. Since it only moved the shoulder back .001 more, I am not too concerned about the chance of a case head seperation.
 
Friends, who were getting started with slow twist 6BR varmint rifles, ignored my advice about ordering a custom fit die from Lynwood Harrell, insisting on buying Redding S type (bushing) FL dies. As luck would have it, the Redding dies were poor matches to their custom chambers, not sizing the base of the case enough with a proper shoulder bump. After realizing that there was no way to adjust their way out of the problem (without creating a safety issue due to excessive shoulder bump), they both ordered the dies that I had suggested in the first place, and their problem was solved.

Very few reloaders actually measure brass, at the shoulder and above the head, before and after sizing. It has been my experience that if the shoulder of a case is bumped .001, and the bottom of the body is slightly reduced, there are no bolt closure problems. From what you have said, I would guess that your die is too large for your chamber. Ignoring the proper amount of bump will eventually lead to a separated case head. I think that you need a new die.
 
When cases are new and soft in the shoulder / neck area a die setting
that achieves .001 bump is great. As the brass work hardens it tends to spring back after pushing shoulders down . This requires a deeper setting to get the .001 bump. With out changing your die setting, anneal a case and
bump the shoulder. Checking this again will reveal that the case body is now
shorter than after a few firings.
 
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