Thread: Weird shoulder bump...

Originally Posted by Edunn

It was indeed new brass before it became once fired brass. Bought it new, loaded it up, fired it, and now it's once fired.

@Edunn
OK, this is what I think is happening.
Firstly, you're not doing anything wrong. And I don't think you are getting a wierd or variable shoulder bump. It's just being new brass some cases haven't stretched as much yet as they will after another firing or two.
Fired brass will conform to your rifle's chamber but being new ( relative to your actual chamber dimensions ) new brass doesn't always stretch to it's full extent until fired at least twice or maybe three times so, in fact, some shoulders are not being bumped just yet but at the moment give the impression of being over bumped. Also, it's possible that even your cases measuring longest to the shoulder now may not yet have stretched to their full limit but have just stretched a little more than other cases so far. So, be prepared to reset your FL die again at some point to give a true shoulder bump. It's possible that if left set where it is now you may be creating excessive headspace which can lead to both primer ignition issues and shortened case life.
What I suggest is that after the next couple of firings of your brass you reset the FL die for the ( true ) shoulder bump at which point the setting should become permanent and not require further resetting.
I say the above based on experience with FL sizing new 375 Ruger brass which had given nil ignition of some CCI primers and I was blaming the primers. I posted my situation here and some knowledgeable members pointed me in the right direction. I was simply over bumping the shoulders, creating excessive headspace, and when, as suggested, I backed the FL die out slightly it was "hey presto", problem solved.

Originally Posted by 30.06king

@Edunn
OK, this is what I think is happening.
Firstly, you're not doing anything wrong. And I don't think you are getting a wierd or variable shoulder bump. It's just being new brass some cases haven't stretched as much yet as they will after another firing or two.
Fired brass will conform to your rifle's chamber but being new ( relative to your actual chamber dimensions ) new brass doesn't always stretch to it's full extent until fired at least twice or maybe three times so, in fact, some shoulders are not being bumped just yet but at the moment give the impression of being over bumped. Also, it's possible that even your cases measuring longest to the shoulder now may not yet have stretched to their full limit but have just stretched a little more than other cases so far. So, be prepared to reset your FL die again at some point to give a true shoulder bump. It's possible that if left set where it is now you may be creating excessive headspace which can lead to both primer ignition issues and shortened case life.
What I suggest is that after the next couple of firings of your brass you reset the FL die for the ( true ) shoulder bump at which point the setting should become permanent and not require further resetting.
I say the above based on experience with FL sizing new 375 Ruger brass which had given nil ignition of some CCI primers and I was blaming the primers. I posted my situation here and some knowledgeable members pointed me in the right direction. I was simply over bumping the shoulders, creating excessive headspace, and when, as suggested, I backed the FL die out slightly it was "hey presto", problem solved.

Awesome, thanks mate! I wondered whether something like this might be the issue but the way you've laid it out makes sense. Just seemed weird that each time I set it at 2 thou for one case it ended up at about 5 thou for all of the rest of them. Will definitely be resetting the sizing die after this firing anyway but thought I'd troubleshoot now to make sure I'm not doing anything silly.