Bumping back the shoulder

[Old Chap]

The term "bumping back the shoulder" seems self-explanatory, but how do you just move the shoulder back, and more importantly in what circumstances?
Thanks.
Phil.

[phaedra1106]

I've just had to do that to all my empty .308 cases.

I bought a new Howa 1500 for my sons upcoming birthday, put in my OAL checking round (case with slots in the neck to allow bullet movement) got the average reading and loaded a dummy round.

I then found the bolt wouldn't close on it. After getting hold of a factory round which chambered and also some RWS cases I got from another forum member which fit I took it to my local gunsmith who tried his cases (very tight) and checked it with headspacing gauges, both fit but he reckons the chamber is right on the tight end and my other .308 (Steyr) is on the large side.

I've got a set of RCBS dies being brought over from the US but meanwhile he milled 20thou" off the bottom of my Lee die to allow up to a full extra turn of adjustment, with an extra 1/4 turn the "bumped" cases now fit the Howa perfectly.

[ovenpaa]

You can also grind 0,50mm off the top of your shell holder to give the same result, do it in a pillar drill if possible on some fairly coarse wet and dry, it takes a while but works very nicely. I have a few shell holders that have been reduced in height in this manner.

[phaedra1106]

He looked at doing that but sticking the die in the lathe was easier or quicker I guess :)

Should have the RCBS die set on Thursday afternoon, my neighbour has been to the US visiting her son and his family, he's in the 10th Mountain Division at Fort Drum, also managed to get hold of a Howa 10rnd mag and conversion kit for me so that's another job to do this weekend.

[dromia]

I like and use the Redding Body dies for bumping back the shoulder, doesn't size the neck.

[Old Chap]

But surely by reducing either the die length or the shell holder height you are making the entire case smaller, not just "bumping" back the shoulder. I am assuming it is a full length sizing die you are talking about? Maybe I have got the wrong end of the stick - is bumping back the shoulder just another way of saying full length sizing?

[phaedra1106]

Yes, but in my case the Lee die was forming the case with the shoulder a couple of thou" longer than the Howa chamber would accept, there's quite a difference in chamber sizes, only way to get an accurate size for your particular chamber is to use a set of gauges. As long as the chamber passes with a set of Go/No Go gauges it's classed as being "in spec" even though (in my case) my two .308s are at different ends of the tolerance.

[rox]

The term "bumping back the shoulder" seems self-explanatory, but how do you just move the shoulder back, and more importantly in what circumstances?
Thanks.
Phil.

The Forster Bushing Bump die allows you to bump the shoulder a small amount without touching the body. You can (optionally) also size the neck with a bushing at the same time. I've not been using one for long, but I plan to use it instead of a Redding comp neck die anytime I'm neck sizing.

..

[kennyc]

He looked at doing that but sticking the die in the lathe was easier or quicker I guess :)

Should have the RCBS die set on Thursday afternoon, my neighbour has been to the US visiting her son and his family, he's in the 10th Mountain Division at Fort Drum, also managed to get hold of a Howa 10rnd mag and conversion kit for me so that's another job to do this weekend.

don't book the whole weekend for it, takes about 3 minutes tongueout

[Old Chap]

Thanks everybody for your illuminating answers.
Phaedra1106, I can see it was a solution to your problem i.e Full Length Sizing Plus.
Rox, may I just ask you then - why are you are using this process when you're neck sizing as your cases must clearly have fitted in order to be fired in the first place? Is there another reason for just moving the shoulder back a couple of thou'?