I've heard and seen this term used here and I would just like someone to define it for me.

I've reloaded for years and have to assume it means something along the lines of full length resizing.

When I load I either partially neck size with a FL die by backing it off or neck size with the neck die.

How is "bumping the shoulder back" accomplished?

First you need to measure before bumping the shoulder back , so you know how much it actually gets bumped .

About .002 is where I like mine to set back from chamber fired cases . Bumping the shoulder

requires a simple adjustment on your full length resizing Die , similar to your neck sizing .

Rather than going full length on the case , just go enough to set that shoulder back around .002

some go .001 others .003 . I like .002 personally . Remember to only fire those cartridges in the rifle

their being fired in . DON'T interchange cartridges in another gun bad things can happen .

rc

Technically, bumping the shoulder means setting the shoulder back a certain distance without sizing any other part of the case. Shoulder bump dies are usually made using the chamber reamer.

A bump die can also incorporate a neck size bushing and/or a base size bushing.

Ray

quote:

Originally posted by Doc224/375:
First you need to measure before bumping the shoulder back, so you know how much it actually gets bumped.

About .002 is where I like mine to set back from chamber fired cases .

Excellent point. I would also recommend that you start with virgin brass or a factory load and then measure the case after it has been fired only once. I use that as my baseline headspace and then back off .002.

Where do you take the measurements from?

From the case head to the mouth or to the place where the shoulder starts?

It seems that using a FL die would defeat the purpose of trying to only use perfectly formed brass for your gun to get max accuracy since it returns the brass to factory specs. Is that what the "bump" die does, retain the shape of your chamber without factory resizing?

quote:

Originally posted by rcamuglia:
Where do you take the measurements from?

From the case head to the mouth or to the place where the shoulder starts?

Headspace is measured from the head to a fixed point on the shoulder called the datum line. You need a headspace gauge/comparator to measure the length.

quote:

Originally posted by rcamuglia:It seems that using a FL die would defeat the purpose of trying to only use perfectly formed brass for your gun to get max accuracy since it returns the brass to factory specs. Is that what the "bump" die does, retain the shape of your chamber without factory resizing?

Although I believe there are bump dies that only move the shoulder, what most people are talking about when the discuss bumping the shoulder when using neck dies is a Redding body die, which is just a standard FL die with an oversize neck bore (the neck is not resized). Obviously the amount of setback is a function of die setup (FL vs PFL)

quote:

Although I believe there are bump dies that only move the shoulder, what most people are talking about when the discuss bumping the shoulder when using neck dies is a Redding body die, which is just a standard FL die with an oversize neck bore (the neck is not resized). Obviously the amount of setback is a function of die setup (FL vs PFL)

I guess it depends on what your definition of "most guys" is.

Competition shooters use dies designed for specific purposes. A bump die only bumps the shoulder, a body die only sizes the body, and a FL die sizes the entire case back to factory dimensions. Some of the features can be combined into a die such as I mentioned in my first post.

You measure shoulder bump with a special gauge and then verify it by trying the case in your rifle (unloaded of course).

The whole idea of these dies is that you only size that part of the case that needs sizing.

Ray

This is the first I've heard of bump dies that do not size the case body at the same time. All the dies I use, which are admittedly not predicated upon what the benchrest crowd uses, size the case body while bumping the shoulder back.

I do know that all (not most) of the discussions I have been a part of or read did not mention bumping the shoulder without sizing the case body at the same time. It would seem to me that if you bump the shoulder back without controlling the case body then you would develop a bulge somewhere.

So, when I P-FL size, I am bumping back the shoulder as well?

Yes Woods has it right .

I personally have never seen a bump die didn't even know they existed !. A body die which does not size the neck

is what I've always used and it sets the shoulder back all the way too full length resizing . IF you don't

set it correctly .Set correctly it will set the shoulder back while sizing the body .


Like Woods said if you don't contain the body dimensions while setting the shoulder back , Where does the

excess length go ? , OUT WARD !.



Belaw also posted a correct reply .

Headspace is measured from the head to a fixed point on the shoulder called the datum line. You need a headspace gauge/comparator to measure the length.


I'm not a BR shooter so maybe they do things differently ! ?.

No R, NOT touching the shoulder and keeping both case and chamber dimensions as close as possible is the reason one goes to partial sizing (with a FL sizer) or to a neck sizing die (the latter is more precise in that it doesn't touch the neck of the case). After several firings, when brass becomes harder to chamber because of the cold working, it's time to send the cases through the body die which will bump the shoulder and squeeze back the case a little bit (less than a FL) in order to facilitate chambering in a specific rifle.

Andre....

That's what I thought. P FL resizing just touches the neck and does not size anything else. When you back the die off and adjust it to size about half of the neck, no shoulder bump happens.

So it IS necessary to get a bump die and bump back the shoulder IF you start to have problems closing the bolt?

After how many firings does this usually take place?

Here's how I define the 3 types of sizing

1. Neck sizing - sizing all or part of the neck and not sizing the case body or pushing the shoulder back

2. Partial Full Length Resizing - sizing all of the neck, sizing all of the case body and pushing the shoulder back so there is still some contact but no severe crush fit

3. Full Length Resizing - sizing all of the neck, sizing all of the case body and pushing the shoulder back far enough so there is no contact at the shoulder in the chamber and enough headspace to prevent minor trash from preventing chambering

Now the range of shoulder movement where PFLR occurs from severe crush fit to no contact is only about .002" to .003". But, I have tried several times to define these terms and no one anywhere wants to get into it and I do not know of any official source that lists the definitions. It's just the way I learned it, mostly from HC (although I hate to admit it ) and later verified when I learned to use all the "thingies" such as the Stoney Point Headspace Gauge.

R,
That's right, if only the neck is (partially) sized, you won't touch the shoulder. After a number of firings (depending on the individual chamber, it may take a just a few or many), the bolt will start to close hard and it's time to bump the shoulder or FL size the case. You can screw deeper your regular FL die (= full neck size + shoulder bump), although the lower case body won't be sized fully. This will not be an issue with all but precision/target rifles. In these, where no compromise is accepted regarding accuracy, it's best to combine neck sizer and body die so as to resize (in turn) all parts of the case, BUT leave the sized portion of the neck untouched. While this may seem a detail; it's not without importance. By sizing only a portion of the neck, true neck sizing allows varying the tension on the bullet, while leaving the base of the neck fireformed to chamber dimension. This way, the case neck is formed in a (faint) bottleneck which allows perfect centering of the bullet nose vis-à-vis the rifling leade and insuring the bullet will engage the rifling straight. I'm not sure if the practical value of this theory can be proved but in precision shooting, lots of things do happen in the shooter's head and having confidence in one's tools and techniques is already 50% of victory