Inconsistent Shoulder Bump

[akinswi]

I sized 15 fired cases to test how consistent my shoulder bump was from case to case.

The results were less than stellar, my shoulder bump range from 2.035 to 2.031. My baseline for a fired case was 2.036. Im trying to achieve a consistent -.003 shoulder bump.

What are some things I can check?

I did anneal these using a torch , I also did not put any case lube on the shoulder. I also do not use an expander ball in my sizer die.

Brass is same manufacturer and from same lot. And has the exact same amount of firings on each case and each case was fired from the same firearm

 

[rg1]

I’ve found consistent case lube is needed to get better shoulder bump. Plus firm force on the press handle at the bottom of the stroke. Single stage presses.

 

[olduser]

Brass hardness I believe has a lot to do with consistent sizing and shoulder bump. It has been my experience that if you anneal after each firing and before sizing you will get better results.

 

[ammo.crafter]

reload

Caliber?

 

[44 AMP]

Have you considered the possibility that the variance is simply due to the individual differences in the cases you measure?

Each one could have a slightly different amount of "spring back" from each other, and still be well within all the specs for the material.

Not saying this is absolutely the case, but I think its quite possible that every case in a given batch isn't absolutely identical.

 

[mehavey]

As noted above, good & consistent case lubrication is first issue.

Second recommendation is to fully size (ram at full stroke), then drop ram about 1/8" and
'bump' it up to top again before removing case.

- 2nd bump doesn't have to fight press spring
- 2nd bump mitigates a against any brass springback.

 

[jetinteriorguy]

I don’t sweat the variance as much as making sure the shoulder is at least .003” shorter on the longest piece of brass. I’ve taken factory ammo and fired 20 rounds, then measured all the cases, I then take the longest piece and bump it .003” and leave it at that. I figure the longest piece from the new ammo represents the most accurate size of the chamber and proceed from there.

 

[akinswi]

ammocrafter,

Caliber is 30-06

mehavey,

I may try that on my next batch, I typically give it 3 seconds of dwell time, But Ill try the 2nd stroke apporach.

Do rotate the case a 1/4 turn on the 2nd stroke?.

44amp,

You may be correct, one experiment I was going to perform was to sort a loaded cartridge by its shoulder bump and see how they group.

Out of the 15 I loaded I did have 5 that were 2.031, Its a very small sample size but will see if any difference

RG1,

The press I am using is a Dillion RL550.

 

[lugerstew]

I have seen this a lot also, kind of aggravating when you are trying for consistency. I think brass quality helps, because I have noticed that lapua brass shoulder bumps are very consistent.
I don't have an annealer.

 

[tangolima]

Everything comes with tolerance. Some perspectives to ponder upon.

Your measurements indicate +/-0.002". A job to machine shop requiring this sort of tolerance, you will need to pay extra. 0.002" out of 2" is 0.1%. Even normal electronic equipment would have difficulty achieving that.

If you made the measurements with caliper, don't forget it comes with its own tolerance. Easily +/- 0.001".

You are actually doing pretty good. Meaning; it would be hard to do any better.

-TL

Sent from my SM-N960U using Tapatalk

 

[Bart B.]

I've had no problems with a few thousandths spread in case head to shoulder reference diameter as long as the bolt closes freely without any binding.

There will be a few thousandths spread in case head clearance to the bolt face.

 

[Shadow9mm]

I would try holding the brass up in the die for 1-2 seconds when sizing. This should ensure you dont short stroke, and reduce spring back.

 

[akinswi]

Shadow, I do have 3 sec dwell time. It amazes me if I dont hold ram down the spring back will actually lower the ram on its own. So I will typically run the case into the die at full stroke and count 1 onethousand 2 one thousand etc. while apply down force so it will not move the ram

 

[akinswi]

I've had no problems with a few thousandths spread in case head to shoulder reference diameter as long as the bolt closes freely without any binding.

There will be a few thousandths spread in case head clearance to the bolt face.

Thanks Bart,

That makes me feel better that im actually sizing everything more consistently than I thought.

 

[mehavey]

Do rotate the case a 1/4 turn on the 2nd stroke?

Negative.
You're not pulling the ram down more than 1/8-1/4"-- just enough to just relieve press spring from the case-wall sizing stress,.
Then back up since shoulder-only produces no stress/spring.

This is a 2-seconds-added operation, no more.

 

[HiBC]

I don't know what measuring tool you are using.

The caliper/clamp on bushing setup is at least SOMETHING,which is a lot better than nothing. Its a practical addition to the Reloaders bench.

Measure and record the same piece of brass 20 times. What variation do you get?

Doing machine work,as tangolima pointed out, plus or minus .003 or so,calipers are efficient. But for .002 or less,a micrometer is what I'd use. Or more sophisticated gauging.
Have you considered an RCBS Precision Mic? You might look one up and research it.
I have a little comparator stand. Its about an 8 inch square of black granite with a post to hold a dial indicator.
It works well with a Wilson bushing case gauge. Just drop the case in the bushing gauge ,stand it on the granite and pass it under the indicator.

I already had the comparator stand and indicator in my machinist tools. And the Wilson bushing was in my loading tools.

 

[Metal god]

All presses will have some flex/stretch/deflection when sizing a case , some more then others . I find that deflection seems to be more in the linkage between the ram and handle rather then the frame of the actual press .

Here is how much my Hornady deflects when sizing a 308 case . You must look for the gap/crack of light between the die and shell holder when sizing a case , You need a load on the press ( actually sizing a case ) in order to know if you have removed the gap and deflection in the press . If you run the die down to just kiss the shell holder . When actually sizing a case there will be a gap , that gap allows for the inconsistency I believe you are seeing .

Die adjusted to just kiss the shell holder with no case in the die

Same die setting but this time sizing a case , note the gap that has appeared

The best way to defeat press deflection is for the die and shell holder to make hard or firm contact at the top of the stroke ( cam over if allowed ). When doing that with a standard shell holder the case gets sized to SAAMI minimum or smaller . The problem most of us run into with that is we often don't want are cases sized down that far from head to shoulder datum and we need to back are die out to get the proper .002 shoulder bump . However as soon as the die is no longer making firm contact with shell holder at top of stroke we introduce that press deflection back into the sizing process .

Depending on the size of the case and or how work hardened it is and your die and shell holder are not making hard contact . The cases can come out longer or shorter ( head to datum ) do to how much the press deflects/flex's on each individual case . When we're only talking .002 the press does not need to give/flex much for it to translate to the sized case .

So if a standard shell holder when making hard contact with the die sizes your case to 1.618 and you want it sized to 1.624 . How can you get that 1.624 bump and still make firm contact between the die and shell holder ? That's where the Redding competition shell holders come in . They come in a set of five and allow you to size your cases longer then a standard shell holder while still making hard contact with the die . They allow you to size your cases longer in .002 increments then a standard shell holder while still making firm contact . Those increments are marked on each shell holder in the set . When used as designed the consistency in which I can size my cases is still a little mind blowing to me . Most of my cases regardless of manufacturer or times fired ( up to 4 because I anneal ) come out +/- .0005 . some cases come out +/- .001 but not many .

They also come in quite handy when sizing for multiple rifles that use the same cartridge . If rifle A needs a shoulder bump to 1.626 and rifle B needs a shoulder bump to 1.624 . You just use the proper Redding competition shell holder with no need to adjust the die . I have not adjusted my dies in years and load for multiple rifles in the same caliber .

I often say competition shell holders are the one thing you must have that you really don't need .

https://www.midwayusa.com/product/101253343

 

[akinswi]

Fortunately I use a DIllion RL550C, so it has a shell plate vs a shell holder. I recently purchased a forster coax so I need to size some on that press see if there is a difference

 

[Metal god]

Yep that’s the problem , I’ve read several people saying they have the same issue when using a progressive press . The Coax should clean that up a bit

 

[lugerstew]

Headspace comparator tool

This is the tool I use to measure my brass headspacing too around -.002 to -.003.
I zero the tool on a fireformed case for the gun I am loading for and then adjust my dies with shims to acquire the proper shoulder setback, it works very well and is accurate to .0005 inch.
My lapua brass shot out of a bolt gun, usually always measures within .0005 to .001, and is very repeatable.
Other brands of brass are more likely to give me .0005 to .003 variability.
I use a RCBS Rock chucker for all my reloading.