Bumping the Shoulder Back??

[Wlscott]

Hello all....

I've been reloading for about three years now, so I'm still pretty new to it. I've always full length resized all of my brass.  

I've heard several references to "bumping or setting the shoulder back" in several different posts.

What exactly does this accomplish, and how is it done?

Thanks for your help.

[Iowegan]

The normal rimless case will enter the chamber until the shoulder touches the chamber. In other words, the shoulder is what stops the case from going farther into the chamber.

When handloaders use a sizing die that only sizes the neck, the shoulder has a tendancy to expand and will not allow the case to chamber easily. The shoulder must be bumped back or sized smaller so the case will chamber without force.

[LouisV]

I've found that doing this cuts the group size by atleast half in one of my rifles. If I knew how to post a pic, I have a target that slows the results. I had some brass that had been neck sized repeatedly and was getting hard to chamber. I disassembled the bolt so I could close it on cases and feel the interfearence. Then used gradualy thinner shims on the shell holder until the bolt would just close. I ended useing a .012" shim. As close as I can measure it moves the shoulder back .002". The nice thing about the shim is that I set up the die to bottom out on the shell holder and get very predictable results. In the loads I tested the standard deviation and extreme spread of velocity were lower in the shells I bumped the shoulder back on. This maybe more from better neck tension in the full length die. I can't think of and accurate way to measure neck tension to find out. I have other rifles that I never have difficulty closeing the bolt no matter how many times I fire and neck size the cases. I haven't tried this comparison yet on them. LouisV

[Rancher]

Instead of full length resizing I measure a fired cartridge with a Stoney Point headspace gauge the set my sizing die so that it only sets the shoulder back 1.5 to 2 thousandths.  It'll make the bolt just a little bit hard to close, but its not something that I cant live with and its never caused a problem for me.  I'd probably be a good idea to make sure that all your brass was trimmed up evenly if you decide to go this route, that way you won't have a problem with a long case not chambering for you.

[Red Neck64]

It is ok to neck size only,if you have a bolt rifle.Autos,leavers,pump do not cam as grate as a bolt rifle does.Brass will last longer when only neck sized.

[Wlscott]

As close as I can measure it moves the shoulder back .002". The nice thing about the shim is that I set up the die to bottom out on the shell holder and get very predictable results.

You do this with a neck size only die?  Where do you put the shim?  Under the shell holder?