Shoulder Bump?

[DynoDan1]

Since I haven't had anyone definitively explain to me how to bump the shoulder back other than what
the books that I have read and the videos I've watched and perhaps most importantly, me being an idiot, I'm not sure what is what.

Here's the problem. I use RCBS dies for resizing my .308 rifle cartridges. Maybe not the best one's
RCBS makes but not the cheapest ones either. If, after firing a round, I measure the shoulder with my Hornady gauges/comparator I come up with, say, 1.6150. I resize it and it now reads 1.6130 did I bump the shoulder back 0.002? Or bump it up 0.002?

 

[Blue68f100]

(fired case) 1.615 - (Sized case)1.613 = 0.002" shorter.

You bumped it back 0.002". If this is a bolt gun I prefer 0.001". But any thing between 0.001-0.002" if fully acceptable. The reason is it normally takes 3 firings for it to fully conform to your chamber, so you still have a margin. I anneal all of mine so making 0.001" is a lot easier to maintain.

 

[JFrank]

We( my SiL &I) have been knocking the case back almost 4k on his 270WSM Savage 11 with about 2k at the CSJ and around the .200 line. Any less shoulder bump just doesn't like to chamber freely when we go to load them.

 

[DynoDan1]

Okay, next question.
Why do I get inconsistent results when I resize?
I measure 1.615 after the cases first firing.
After FL sizing I get 1.6125's and then I get 1.617's and everything in between.
And get this. After measuring the shoulder dimension of, say 1.615 after the case has been fired, then I resize it and it's now 1.617.
Die is set to just contacting the ram/shell holder with a slight cam-over.
Die is clean and not damaged or worn out, about 2.5 years old
Shell holder is less than 6 months old.
Press is a Hornady Lock-n-Load about 2 1/2 years old.
Measuring instrument's are Mitutoyo calipers.
Hornady comparator gauges.
Any ideas, suggestion's, remedies?

 

[The Glockodile]

Lots of areas to look.

To draw an analogy - you're measuring with jeweler's tools while performing sizing actions with crude, blunt instruments. In addition (no offense meant), some practice / training is required as far as consistent measurements are involved. Just like divvying out snot through an Eppendorf - it's not just twisting a dial to a specific number.

I vaguely recall them being termed "uncertainties" - and there was a certain arithmetic followed in adding them up.

The "slack" adds up when you're using a regular, articulated press - be it a Forster, RCBS, etc. It's a huge, crude tool with lots of play in it. Though there's some technique which can minimize such variance - the inconsistent values you'll encounter are inherent to the design of such presses.

 

[Blue68f100]

The brass is work hardening making it harder to size. Case lube can make a big difference in how the brass is sized. There are thin film and thick film lubes. If you fell excess resistance add more lube. There is no reason to muscle them.

Annealing will make it more uniform when it come to sizing.

 

[AJC1]

Are these cases mixed brass or a single head stap lot that you track. Sorting brass and annealing will give more consistent results.

 

[Slamfire]

If, after firing a round, I measure the shoulder with my Hornady gauges/comparator I come up with, say, 1.6150. I resize it and it now reads 1.6130 did I bump the shoulder back 0.002? Or bump it up 0.002?

What type of rifle are you using. The Comparator will not measure true chamber size on a gas gun, because the gas gun stretches brass during extraction.

Cases fired from a M1a.



I trust the measurements these gauges provide me.





Comparators are useful only when the bolt gun you are reloading for, does not use a cartridge for which there is a cartridge headspace case. Such as the 7.5 X 55 Swiss.

 

[AJC1]

What type of rifle are you using. The Comparator will not measure true chamber size on a gas gun, because the gas gun stretches brass during extraction.

Cases fired from a M1a.

View attachment 1024623

I trust the measurements these gauges provide me.

View attachment 1024624

View attachment 1024625

Comparators are useful only when the bolt gun you are reloading for, does not use a cartridge for which there is a cartridge headspace case is available. Such as the 7.5 X 55 Swiss.

I never even considered a gas gun good point.

 

[txtaxman]

I use RCBS dies for resizing my .308 rifle cartridges. ........ If, after firing a round, I measure the shoulder with my Hornady gauges/comparator I come up with, say, 1.6150......

Why do I get inconsistent results when I resize? I measure 1.615 after the cases first firing. After FL sizing I get 1.6125's and then I get 1.617's and everything in between. And get this. After measuring the shoulder dimension of, say 1.615 after the case has been fired, then I resize it and it's now 1.617.
Die is set to just contacting the ram/shell holder with a slight cam-over.......Any ideas, suggestion's, remedies?

Turn your sizing die in about 1/8 to 1/4 turn and try again. You need enough cam-over that the top of the shell holder touches the bottom of the sizing die at the top of the sizing stroke while actually sizing a case. A case increasing in base to datum length when being sized is an indication that the die needs to be turned in more.

As you have discovered, some cases resist sizing than others, even from the same lot.

 

[DynoDan1]

Lots of areas to look.

To draw an analogy - you're measuring with jeweler's tools while performing sizing actions with crude, blunt instruments. In addition (no offense meant), some practice / training is required as far as consistent measurements are involved. Just like divvying out snot through an Eppendorf - it's not just twisting a dial to a specific number.

I vaguely recall them being termed "uncertainties" - and there was a certain arithmetic followed in adding them up.

The "slack" adds up when you're using a regular, articulated press - be it a Forster, RCBS, etc. It's a huge, crude tool with lots of play in it. Though there's some technique which can minimize such variance - the inconsistent values you'll encounter are inherent to the design of such presses.

Okay, thanks for the advice.
Just a side note. My last job, (17 years) I was a senior lead quality assurance inspector for a large medical device company.
I was required to use basic measuring tools up to and including high precision digital/optical measuring devices up to tolerances of 0.00001mm.
So knowing how to use a caliper/micrometer is not an issue.
I've considered the "play" involved with the components of a press. It involves, to some degree, a term called "tolerance stacking".
Of which doesn't explain the amount of plus/minus deviations I'm encountering. I do understand that tolerance stacking
is to be expected to some degree, I just don't think I should be seeing as much as I do see.
I'd rather not resort to purchasing another set of dies that are of premium quality as I have been told the ones I currently have are decent.
I do have a premium Hornady match grade die set I bought in the beginning of my reloading journey and I have had nothing but trouble with it and it definitely is not worth the extra $60 I paid for it over the cost of the RCBS set I use.

 

[DynoDan1]

The brass is work hardening making it harder to size. Case lube can make a big difference in how the brass is sized. There are thin film and thick film lubes. If you fell excess resistance add more lube. There is no reason to muscle them.

Annealing will make it more uniform when it come to sizing.

I don't think the brass has been work hardened.
So annealing at this point is moot.
This is brass that's been fired just one time.
I use Hornady unique case lube. I haven't had to "muscle" my brass since switching to this lube, ever. And just dab gets the job done.
This stuff is great!

 

[DynoDan1]

Turn your sizing die in about 1/8 to 1/4 turn and try again. You need enough cam-over that the top of the shell holder touches the bottom of the sizing die at the top of the sizing stroke while actually sizing a case. A case increasing in base to datum length when being sized is an indication that the die needs to be turned in more.

As you have discovered, some cases resist sizing than others, even from the same lot.

I believe I have set the die correctly as you described. There indeed is enough cam-over...I think!
I will reset them again as you described and try again.
Thanks for your help.

 

[DynoDan1]

I never even considered a gas gun good point.

I'm using a .308 bolt action rifle.

 

[DynoDan1]

What type of rifle are you using. The Comparator will not measure true chamber size on a gas gun, because the gas gun stretches brass during extraction.

Cases fired from a M1a.

View attachment 1024623

I trust the measurements these gauges provide me.

View attachment 1024624

View attachment 1024625

Comparators are useful only when the bolt gun you are reloading for, does not use a cartridge for which there is a cartridge headspace case. Such as the 7.5 X 55 Swiss.

I am using a device like you pictured. It comes in handy, letting me know if my resized cases will chamber
I shoot a .308 bolt action rifle.
I don't think a comparator gauge tool measures chamber size...does it?

 

[DynoDan1]

Are these cases mixed brass or a single head stap lot that you track. Sorting brass and annealing will give more consistent results.

They are Lake City brass.
All have the same head stamp.
The ones I am currently writing about have only been shot once.

 

[JFrank]

I believe I have set the die correctly as you described. There indeed is enough cam-over...I think!
I will reset them again as you described and try again.
Thanks for your help.

Brass always seem to grow just before they bump, do your resized cases chamber freely or have a slight to heavy resistence ?

 

[AJC1]

They are Lake City brass.
All have the same head stamp.
The ones I am currently writing about have only been shot once.

The thicker cases may be more springy. I have focused my efforts on testing win, remmington and privi so far. The rem are my favorite so far and the Winchester needed annealed immediately. Privi was all over the map in case weight and just didnt meet my consistancy requirements. I gave my LC to a friend who loves them, so no direct experience with those other than weights and consistancy.

 

[Slamfire]

I am using a device like you pictured. It comes in handy, letting me know if my resized cases will chamber
I shoot a .308 bolt action rifle.
I don't think a comparator gauge tool measures chamber size...does it?

A comparator works well for single shot rifles and bolt action rifles. Can't say I have tried to measure cases out of Lee Enfields, that rifle with its rear locking lugs is like a trampoline. But for rigid, front locking, manual rifles, the base to shoulder distance is "the chamber measurement" give or take brass spring back.

In my opinion, just try to get a nominal 0.003" shoulder push back. Because of brass springback, and lube thickness on the case shoulder, that 0.003" will be an average. You do not want 0.006" setback as that will cause case separations for many types of brass.

And, I use small base dies for the cartridges that have them. If you are technical, then you can understand work hardeness, spring back, and chamber clearance.

There are a number of variables involved, but you want the case to be smaller than the chamber on feed, and then you want the case to be smaller than the chamber upon extraction. If the case is clinging to the case walls, it will stick. And you may have to take a cleaning rod to get it out of the chamber.

You can follow these charts.






So, full length resize, push the shoulder back about 0.003". take into account the process is not perfect, case base to shoulder will vary, but by all means, prevent your cases from having an interference fit upon chambering.

 

[jmorris]

If, after firing a round, I measure the shoulder with my Hornady gauges/comparator I come up with, say, 1.6150. I resize it and it now reads 1.6130 did I bump the shoulder back 0.002? Or bump it up 0.002?

The length is .002 shorter than it was previously to, so “back” would be appropriate, if it was longer. “Blow out” is the term generally used to make shoulders further away from the case head, than they were previously. I suppose if you were holding the case with the head towards the sky and the mouth, towards the ground, you would have bumped it “up”.

I am using a device like you pictured. It comes in handy, letting me know if my resized cases will chamber
I shoot a .308 bolt action rifle.
I don't think a comparator gauge tool measures chamber size...does it?

A case gauge is handy to have, especially if you have many firearms chambered in the caliber. You make all of your ammunition to fit a minimum dimension and it will run in everything.

If all you have is one bolt action rifle, I find this method works well and cases last much longer than sizing to minimum SAAMI. Pretty much the same one I use for benchrest rifles too but have to keep that ammunition for that rifle.

 

[DynoDan1]

Brass always seem to grow just before they bump, do your resized cases chamber freely or have a slight to heavy resistence ?

They chamber fairly freely after resizing, pretty much like factory ammo does.

 

[JFrank]

Ok , just checking..