bumping back shoulder?

[kennedy]

what does it mean and how do you do it?

 

[rcmodel]

In simple terms?

You take a fired & expanded case, and back the sizing die out just enough from FL sizing to just 'bump back' the shoulder on the case enough to give you minimum headspace in your rifle for the next re-loading cycle.

Without full-length sizing the whole case back to factory dimensions again.

rc

 

[witchhunter]

When neck sized rifle brass is fired it tries to expand any direction it can, lengthways is the only feasible way as the chamber size limits other growth. It tries to grow out the barrel. After a while the brass is hard to chamber as it has grown to fully encompass the chamber size. Now, you have to resize the shoulder back toward the base, "bump it back" with a full length sizing die in order for it to fit the chamber without difficulty.

 

[witchhunter]

Dang, RC, while I was writing this essay on metallurgy, you made it too simple, I was trying to sound smart!

 

[Walkalong]

http://www.thehighroad.org/showthread.php?p=6270171#post6270171

http://www.thehighroad.org/showthread.php?t=734058

 

[rcmodel]

I was trying to sound smart!

And you did.

I was just too lazy to go into it in greater detail.

But you did a fine job, I would recommend to anyone!!

rc

 

[USSR]

...you have to resize the shoulder back toward the base, "bump it back" with a full length sizing die in order for it to fit the chamber without difficulty.

Or with a body die, which is what I use.

Don

 

[ranger335v]

"Shoulder bump" is part of the normal effect of FL sizing. A so-called "bump die" (more correctly, it's a body die) is an FL die that's been neck reamed so it doesn't size the case neck.

 

[gamestalker]

It's important to make sure you don't "bump" them back more than is necessary to facilitate proper chamber fit, other wise premature head separations will present. Excessive head space can even cause new brass to experience separations. I consider more than.002" to be the max bump in this respect.

What I usually do is check all my brass in the chamber, and then only bump those that are difficult to chamber. This helps to extend brass life by not over working it in the chamber, or the press.

GS

 

[Rangemaster]

Back off your sizing die and mark the shoulders of your test brass with a sharpie.