Shoulder bump

[Crunchy]

Can someone explain the importance of bumping the shoulder back .002.  As long as you bump them all the same why is 2 thou what everyone refers to?  I back my resizing die out at least one full revolution to get close to .002 and that makes me thread the decapper 3/8th of a inch or so out past the die to get the cases deprimed.  Am I really getting full length resizing with the die backed out this far? 

[b23]

Bumping the shoulder back 2 thou is fine once the brass has reached its max shoulder length in relation to the chamber, but you really don't want to be arbitrarily bumping the shoulder back 2 thou until it has reached its max length or you'll end up with a lot more headspace than you think and that can not only lead to accuracy issues but it can cause premature case separation.

Generally, it takes a relatively firm cam over to bump the shoulder back and you typically can't get that if the sizing die isn't touching the shell holder.

[Magnum_Willys]

The shoulder will move to the front of the chamber by stretching the lower part of the case.  This thins the lower part of the case.  The further you stretch it each firing the fewer times you can reload before head separation.   Accuracy is also enhanced sometimes with minimal clearance. 

Depending on fit of your die to chamber a 2 thou bump may not resize the round at all and you barely feel resistance or it may take a firm camover resizing the whole brass. 
You may have to bump a lot more than .002 to get round to chamber but no reason to bump more if your die works at that. 

[Jonathan_S]

I have no idea why people say .002

Most guys probably just bump them enough to get them chambered without issue

[Oh Mah]

i read that .002 is optimal because that .002 relief will allow for easy loading into the chamber and when it fire forms again with next shot it will swell up and take that .002 and then come back down to the .002 relief again..005 or more from fire form will cause shell to keep moving out and need the constant over resizing to fit in chamber taking away shell life.

That said i wish i knew how a person is supposed to get this magical .002  what tool or technique?

[Crunchy]

I was just wondering why the importance of .002.  I might do a little experiment with my next batch of brass that needs resizing and see if I notice a difference.

[hogslayer]

If you bump to much you will get thinning of the web after multiple firings.  Don’t always trust your bump gauge as shoulder angles are different and where the gauge lands on the shoulder can be different.  Best way is to remove shroud and firing spring assembly, punch out ejector,  size a case and try to chamber. Keep changing out shell holders if you have the reading set. If not keep screwing die down and measuring bump.  You’ll get to where the bolt falls freely until about the last 1/4.  This is considered a slight crush on close.  I like to be .0015 past that.  Usually ends up between .002-.003 according to the gauge.  If brass is harder to close it will exhibit bolt lift once fired.

[Yondering]

I was just wondering why the importance of .002.  I might do a little experiment with my next batch of brass that needs resizing and see if I notice a difference.

.002" in most cases is about the closest you can reliably get to "zero" shoulder bump while still being able to chamber all rounds. If you're loading for rough conditions or a semi-auto you might consider a little more bump.

It's not that .002" bump is some magical number, the point is to achieve minimum shoulder bump while still full length resizing. If you screw the die down to the shellholder per generic sizing die instructions, in many cases you're sizing too much and creating excess headspace, which shortens brass life and also causes false pressure signs.

[Karl Blanchard]

I redneck it. Small adjustments until a piece chambers easily. I've lost track of how many different rifles I've loaded for and every time I actually measure the end result it's always about .002   like Yondering said, gas guns are a different beast.

[BULLBLASTER]

I used I redneck it. Small adjustments until a piece chambers easily. I've lost track of how many different rifles I've loaded for and every time I actually measure the end result it's always about .002   like Yondering said, gas guns are a different beast.

adjust it so the sized brass just chambers easily by feel. I had done alll of mine that way and then bought the Hornady gauges to do it better. All the ones I had done were right at .002.
I don’t pay any attention to if the shell holder touches the die or if there is cam over or anything like that.

[jasnt]

I used I redneck it. Small adjustments until a piece chambers easily. I've lost track of how many different rifles I've loaded for and every time I actually measure the end result it's always about .002   like Yondering said, gas guns are a different beast.

adjust it so the sized brass just chambers easily by feel. I had done alll of mine that way and then bought the Hornady gauges to do it better. All the ones I had done were right at .002.
I don’t pay any attention to if the shell holder touches the die or if there is cam over or anything like that.

[b23]

FWIW, don't always assume the brass has reached zero headspace upon every firing, especially, with new brass.  Often, new brass will be a fair bit shorter at the shoulder than your chamber and it'll take more than one time firing for the brass to reach zero headspace. 

Like I said before, bumping the shoulder back 2 thou is fine as long as the brass has reached a point of zero headspace, but if it hasn't, you'll have more, possibly a lot more, headspace than you think if you just arbitrarily always bump the shoulder back 2 thou.

For Rem 700's it's really easy to strip the bolt of the firing pin assembly and ejector, then take a piece of unsized brass that has been fired in that gun and slide it up into the chamber.  Once it's been pushed all the way forward let go of the bolt hand and see if it falls all the way down on its own.  If you let go of the bolt handle and it closes and falls all the way down on its own without stopping, the brass hasn't reached zero headspace yet.  If the bolt closes most of the way but stops just a little short of clanking against the receiver, the brass has reached zero headspace or maybe even a tick more than zero and at that point it's ok to push the shoulder back 2 thou.  If the bolt handle falls closed and clinks against the receiver, I wouldn't push the shoulder back.  Remember, this method really only works very well if you completely strip the bolt of the firing pin assemble and ejector.  if you leave the ejector in, it can give you a false reading so I always completely strip the bolt so there is no guessing.

[Crunchy]

Guess I need to learn how to remove the ejector.  Firing pin assembly is pretty easy.  I am on the second firing of new brass, so I should be close.

[2labs]

i read that .002 is optimal because that .002 relief will allow for easy loading into the chamber and when it fire forms again with next shot it will swell up and take that .002 and then come back down to the .002 relief again..005 or more from fire form will cause shell to keep moving out and need the constant over resizing to fit in chamber taking away shell life.

That said i wish i knew how a person is supposed to get this magical .002  what tool or technique?
[/quote


Scotch tape. Magic tool.

[buckfvr]

Or you can measure immediately after firing to get a somewhat better idea compared to measuring cold brass........its important to have them all set back the same as uniformity is what youre after in the first place, so .002 to .004 is fine so long as they are all the same, just like trim to length and neck wall thickness......all the same.

[Yondering]

Or you can measure immediately after firing to get a somewhat better idea compared to measuring cold brass........its important to have them all set back the same as uniformity is what youre after in the first place, so .002 to .004 is fine so long as they are all the same, just like trim to length and neck wall thickness......all the same.

It doesn't matter. Case to case variation is greater than any difference you'd see there. The point is to set the shoulder back as little as possible while still sizing enough so all cases chamber and extract easily. If you're using mixed brass or not annealing, setting shoulder bump to .002" average will result in some variation, probably .001"-.004" if things are working right, or a lot more variation if the brass is really inconsistent.

Setting shoulder bump is accomplished by adjusting the sizing die body down until it bumps the shoulder back the specified amount, rather than jamming it all the way down to the shellholder without measuring. With some cartridges and dies you'll end up with the die very close to or at the shellholder, but with others you'll have it backed off a bit.

[Fl0und3rz]

I always understood it to be an alternative to neck-sizing fire-formed brass intended to be used in the same rifle chamber, with 0.002" being a rule of thumb to ensure reliable chambering.  I use a Lee Collet die to neck-size, if I am looking to achieve the benefits of neck-sizing.

[Yondering]

No, it's not neck sizing. The .002" shoulder bump is full length sizing, it just involves measuring to make sure you're not bumping shoulder back more than necessary.

You may be thinking of partial sizing with a full length die, where a portion of the neck is unsized and the shoulder is not touched at all. That can work well too, but is not what we're talking about here.

[Fl0und3rz]

I think we are saying the same thing from a different angle.  Maybe not.  Wouldn't the neck be sized at least partially by the sizing die if you're hitting the shoulder?  But I guess you wouldn't get any shoulder bump with neck-sizing, if that is what you are after.

I admit I don't fire enough bolt action (still working on 50 or so fired/necked cases) or super-mega-magnums having enough case stretch to bother.  Most is either FL sized or neck-sized.

[BULLBLASTER]

Super mega magnums don’t have any more or less case stretch than any other cartridges. Case lengthening is a product of head clearance not powder burned. With small shoulder bumps or neck only sizing there shouldn’t be any or very minimal case stretch. I have some 300 win brass on its 6th during that has never been trimmed. Has only stretched .006 since its first firing.

[Yondering]

I think we are saying the same thing from a different angle.  Maybe not.  Wouldn't the neck be sized at least partially by the sizing die if you're hitting the shoulder?  But I guess you wouldn't get any shoulder bump with neck-sizing, if that is what you are after.

I admit I don't fire enough bolt action (still working on 50 or so fired/necked cases) or super-mega-magnums having enough case stretch to bother.  Most is either FL sized or neck-sized.

If the die bumps the shoulder, the neck and the rest of the case are all fully sized. It is not possible to bump the shoulder with a full length die without fully sizing the neck. The .002" shoulder bump discussed here is correct full length sizing for your chamber; in many cases running the die all the way down to the shell holder is excessive sizing but is a one-size-fits-all approach for generic sizing die instructions.

As Bullblaster said - case stretch is not just (or even mostly) the territory of bolt actions or magnums, in fact weaker actions like a 30/30 lever gun or most semi-autos benefit just as much or more. Pretty much all bottleneck cartridges benefit from correct sizing.

[jasnt]

I think we are saying the same thing from a different angle.  Maybe not.  Wouldn't the neck be sized at least partially by the sizing die if you're hitting the shoulder?  But I guess you wouldn't get any shoulder bump with neck-sizing, if that is what you are after.

I admit I don't fire enough bolt action (still working on 50 or so fired/necked cases) or super-mega-magnums having enough case stretch to bother.  Most is either FL sized or neck-sized.

If the die bumps the shoulder, the neck and the rest of the case are all fully sized. It is not possible to bump the shoulder with a full length die without fully sizing the neck. The .002" shoulder bump discussed here is correct full length sizing for your chamber; in many cases running the die all the way down to the shell holder is excessive sizing but is a one-size-fits-all approach for generic sizing die instructions.

As Bullblaster said - case stretch is not just (or even mostly) the territory of bolt actions or magnums, in fact weaker actions like a 30/30 lever gun or most semi-autos benefit just as much or more. Pretty much all bottleneck cartridges benefit from correct sizing.

: yeah: