What is bumping shoulders and how do you do it?

[TheSilverFox]

I have a redding type s bushing die,full lenght resize) for my 308 cal.

I was reading in the articles section,Froggy Part II -- Reloading) that he bumps his shoulders .001 to .002.

How do you adjust your die for that and how do you measure the results?

 

[flatlander]

"Bumping" the case's shoulder simply means pushing it into the FL die far enough to move the shoulder back. The simplest & most consistent way I've found to keep track of what you're doing is to use a Stoney Point headspace gauge to measure a case's headspace before & after sizing.

Over the years, I've not found very many die sets that would produce very much 'bump' - most shellholders are too thick or tall to push a fired case far enough into the die to produce enough bump to allow easy chambering of loaded rounds in a custom chamber that's been cut to minimum specs. Some guys machine a few thousands off the bottom of their sizing die to get around this, but I prefer to grind or mill a few thou off the topside of the shellholder - it's a lot less expensive to replace a shellholder than a ruined FL die if you screw up, and shellholders are typically a lot easier to machine than a hardened die.

 

[ballistic64]

You should always anyway,but keep your bolt lugs greased when you start experimenting with "bumping/partial resizing.

 

[Forum Boss]

The other thing to keep in mind that some dies won't move the shoulder much at all unless you set the press to "cam-over". If there is a lot of slop in the press set-up, you can screw the die all the way down 'til it touches the shellholder,at max lift) and the shoulder won't move.

In this situation, what you want to do, is to raise the ram ALL the way up, then screw the die down to touch.

Then, LOWER the ram and screw the die down in 1/8th turn increments, checking for bump amount along the way. I have one turret press with enough slop that I have to position the die 1/3 turn below "just touching". At that setting, the press takes out the internal slop and the case shoulder moves about 0.0015".

 

[AndyW]

I have a question about this as well;

I FL size only when I have considerable resistance closing the bolt, and with my hunting ammo. With my reloading set-up, dies, press, etc.. For me to get the shoulder bump it is no different than just FL sizing. I always read of guys just bumping the shoulder, but I have to cam-over my press as the Mod. says, so what is the difference? BTW, I measure with the Stoney point headspace gauge, so this is not an assumption just based on "feel"

Running brass far enough into the FL die to get shoulder contact is also squeezing the whole case back to spec. anyways???

What I think is with a FL die, to get this bump people talk about you are just FL sizing. I have read about a Harrels bump die, but I believe this is different than a FL die? I would assume it does not squeeze the case body back to spec, but just bumps the shoulder back.

What am I missing?

 

[Craigyboy]

I had my gunsmith make me up a bump die for my tac20, it is made to just bump the shoulders and not touch any other part of the case, forester make a similar bump die, its essential you know youre headspace measurement on your case before you start, generally 1-2 thou is plenty, the best way to set it up though is take out the firing pin out of the bolt so the bolt is unsprung, chamber a tight fired case a few times to get a feel, then work the bolt on an empty chamber a few times to get a feel, now set up your fl sizer or bump die and just to barely touch the shoulders, try the case in the chamber taking note of how it felt to chamber, keep adjusting the die down slowly bumping tiny bit at a time and trying it in the chamber until the bolt just feels stiff on the last half of caming down on the bolt, this should be just about right but also keep and eye on it with the vernier calipers as you go.

 

[ReedG]

I agree with AndyW.

If you run a case far enough into an FL die to bump the shoulder, you have full-length sized the case.

The only way I know of to truly bump the shoulder of a case is with a die made specifically for that. Mine is a bushing die made my Jim Borden with the same reamer he used on my barrel. It sizes the neck by whatever size bushing I use, plus pushes the shoulder back .0015-.002".

Forster has just started marketing a line of true "shoulder bump" dies called "Precision Plus Bushing Bump Sizing Dies. These should be a nice addition to the market.

 

[Rustystud]

Elementary Bumping shoulders....

For the purpose of this conversation I will use Redding Dies as my example.

There are Full Length sizing dies. There are exactly what they say they are. Dies that size all the outside surfaces of the case.

There are Neck Sizing only dies. They only size the neck portion of the case.

There are both neck bushing and non bushed versions of the above described dies.

In my humble opinion neither of the above dies should bottom out on the shell holder. There should always be just a little clearence between the die and the shell holder. If not you have run out of adjustment.

Redding makes another die that is called a body die. It only sizes the sides and web of the case. This die should be adjusted to bottom out on the shell holder.

If the Full length and Neck Sizing die bottom out on the shell holder then they may not push the shoulder back the .001 to .002 needed to take the case back to its pre fireformed state.

Fired cases expand in all directions including length. This is call case steretch. Compressing the cases to much will just exercise the brass and make it have a shorter service life. It also adds in a factor to interfere with your best accuracy. There is a happy median to be found somewhere.

I am sure there will be a hail storm of comments to what I have just said.

Again there are many ways to skin the cat.

Rustystud

 

[TheSilverFox]

have you guys found it increases accuracy?
In other words, does it reduce runout?

 

[ballistic64]

A case that has been fired in the chamber is as straight as its ever going to be.The least you can do to it after that,which is neck sizing only,and still have it chamber decently is as good as it gets.Thats not to say you wont have to use other means of sizing you case eventually.In my 300saum,,custom reamer),I can neck size only about five times before I have to use a body die.

 

[ReedG]

I don't think the shoulder bump has anything to do with accuracy or run-out. I believe it originated in the world of the 6 PPC and "point blank" benchrest. The PPC is regularly used with loads that are off the scale as far as pressure goes and the cases are never full-length sized. As they keep stretching and hardening, the problem becomes closing the bolt on a loaded round. It was not unusual to see guys literally bang the bolt closed with their fist or a good whack with the palm of their hand! I heard an old-timer say that if you can close the bolt easily, you're not loading hot enough. Whatever, the shoulder bump came about to push the shoulder back a minimal amount to make it possible to close the bolt without brute force. Lots of the BR shooters today have dies that bump the shoulder on every resize; some only do it when the bolt starts to close hard.

 

[AndyW]

I have only been at this a few years, now it is a full blown disease I have. Reading and talking to reloaders and shooters as much as I can it surprises me how many talk of "bumping the shoulder" by just adjusting their FL die. You guys have confirmed what common sense has always told me, it is impossible to just bump the shoulder this way. It is just full length sizing.

Great site, a great resource!

 

[tuck2]

Take a look at the Redding Competition Shellholder Set of five shell holders that can be used with a FL die. The shell holders are .002, .004, .006, .008, and .010 of an inch thicker than a standard 0.125 inch shell holder.

 

[flatlander]

Shoulder bump dies that don't size any other portion of the case have been pretty much a custom made item. I've never considered bumping shoulders as a separate operation with most of my rifles - rather as just another part of FL sizing a case.

For example, when shooting the rapid-fire strings in a highpower match, the last thing we want is a box of ammo loaded in cases that have their headspace dimension set long enough to cause any problems whatsoever closing the bolt. With a bolt action match rifle or a gas gun, experienced HP shooters always set their FL dies to bump shoulders back a couple of thousandths when preparing ammo for the rapids.

There's no mystery to it - you've either got your FL die set up to bump the shoulders while sizing, or you don't. The only sure way to tell what you're doing to case shoulders is to measure the headspace dimension before & after sizing with a gauge or tool designed for that purpose. As I mentioned in my first reply, most factory FL die sets won't bump shoulders of cases fired in a chamber with anywhere close to minimum headspace back a measurable amount without modifying either the shellholder or the die itself.

 

[DRGreysun]

FWIW, I'm sure most of you are using custom FL dies cut with your chamber reamers. I also wonder how many shooter who ask questions here use non-custom FL dies and factory cut chambers.
I'm not a BR shooter, however I do read this forum and glean every little bit of info I can from it. What I know and many of you know this too. The difference between a factory cut chamber and a custom cut chamber and die is like night and day. I'm not new to reloading and I learn new stuff everyday. What I have learned is that brass is most likely made to min. SAAMI spec. and most factory chambers are cut to max. SAAMI spec. Even then they can vary a great deal from one manufacture to another. As well as one chamber to another within the same manufacture. Plane and simple all things are not created equal. Brass that 'lasts forever' in a custom cut chamber can turn to junk with one hot load in a factory cut chamber. Neck size, spit necks etc. will be the last to cause a problem. The head will stretch first and show up as loose primer pockets. Another thing with non-custom FL dies and bumping shoulders, there is no such thing as bumping the shoulder back .001-.002". I reload 30.06 for a post 64 Mod. 70 and have found that when my bolt gets stiff on closing and I want to 'bump the shoulder back' .001-.002" I am actually moving the shoulder .010 to .012". Not to mention working the sides back to near SAAMI spec. It's like squish, squirt and crunch which is really hard on the brass and doesn't take much to work harden it from web to neck. I know this is a BR forum and for BR discussion but I thought I would throw this out for those, like myself that visit here looking for the straight skinny from the 'experts' in accuracy shooting. Thanx for your time!

D R

 

[DRGreysun]

CatShooter,

Thanx for you input, I do not agree with all you have pointed out. When I referred to 'head stretch' I was thinking diameter and should have use 'head expansion' perhaps. Again, thanx for your input and Happy Holidays.

D R

 

[DRGreysun]

By the way, I found the following rather offensive:

I know this is a BR forum and for BR discussion but I thought I would throw this out for those, like myself that visit here looking for the straight skinny from the 'experts' in accuracy shooting

Gunamonth,

No offense intended, I'm here to learn just as most are!

Here's a little project for you, next time you feel the need to FL resize your brass try this. Measure the shoulder/head space length before you run the case into the die. Stop just short of the shoulder and remove the case and measure it again. I'm sure you will find it's longer by several .000". Add .001-.002 to your measurement and you will have your total shoulder bump. I would think a shorter case 22-250 or 6BR etc would be less then say a 308 or 30.06 etc. The point is as the die squeezes the case the brass moves toward the shoulder and has to be pushed back an equal amount plus whatever you have your bump-back is set to.

D R

 

[tripcrow]

Where’s the brass go when you bump a shoulder with a die like the new Forster bump & neck bushing? With a FL die, that also pushes the sides, the brass pretty much has to travel up and stretch the neck longer. But without body support, you’d think the Forster would push out on the body as well as stretch the neck.

 

[Dgd6mm]

Most of us have the tools to set up shoulder bump. Excessive shoulder bump will eventually lead to headcase separation. If you set a die up per most manufacturing specifications you'll be over bumping and not even know it without proper measuring tools. It's no big deal as you put it until one comes apart in your chamber.

 

[morpheus]

15 years. A new record?