Too much bump?

[Texas Solo]

How much shoulder bump is considered too much?
When I set up my die I got butter smooth chambering. I have .002 headspace. After working up the load I'm very pleased with the ammo performance. I get .250" or less at 100yds, and .500 moa at 600yds.
I never checked how much bump I had.
I just did. From a fired case to a sized case, I have. 007" bump. It seems excessive to me, but I've read that some are over .010".
I'm so happy with my ammo performance that I'm hesitant to change anything.
What will excessive bump do? Reduce brass life?
Affect accuracy?

6 Dasher, Alpha brass, 105 Berger, Varget.

 

[drop_point]

You are likely reducing your brass life. Additionally, once you start using less bump, you may need to tweak seating depth just a wee bit.

 

[NorCalMikie]

Fire a round, See if the brass will re chamber with no resistance. If it does, size the neck WITHOUT pushing the shoulder back.
When it starts getting tight to chamber, THEN size the brass being careful NOT to push the shoulder back too far. .002 is a good # to work for.

 

[ShtrRdy]

I'd say if it's working well for you, stay with it. Brass life will be a little shorter but you're having fun.

 

[Rob01]

Something isn't right. What do you mean you have .002 headspace? You aren't bumping .002" if you are .007" longer after firing.

If you have .007" of growth in your case after firing you are bumping back way too much. Measure the fired case and adjust your sizing die so that you are only bumping .002". That will extend brass life from not over working the brass.

 

[Kracken McGraw]

How much shoulder bump is considered too much?
When I set up my die I got butter smooth chambering. I have .002 headspace. After working up the load I'm very pleased with the ammo performance. I get .250" or less at 100yds, and .500 moa at 600yds.
I never checked how much bump I had.
I just did. From a fired case to a sized case, I have. 007" bump. It seems excessive to me, but I've read that some are over .010".
I'm so happy with my ammo performance that I'm hesitant to change anything.
What will excessive bump do? Reduce brass life?
Affect accuracy?

6 Dasher, Alpha brass, 105 Berger, Varget.

Are we getting back to Guffy terms now?
.002 headspace but .007 bump?

 

[T.Rhodes]

That much bump, as @drop_point said, adversely affects case and, you may get case head separations after repeated loadings. The brass has to stretch to fill that .007" head space.

 

[Texas Solo]

Are we getting back to Guffy terms now?
.002 headspace but .007 bump?

To clarify:
I gave it .002 headspace when I installed the barrel.
Shoulder measurement is post firing vs sized.

 

[Rob01]

To clarify:
I gave it .002 headspace when I installed the barrel.
Shoulder measurement is post firing vs sized.

Sized or new? If sized you are doing it wrong and need to adjust your die. If new then it's not a big deal and just adjust die off of fired case for .002" bump.

 

[BoydAllen]

You need to become familiar with how case head separations happen. There is plenty of information out there on that subject, both on this forum and on the internet. Google is your friend. If you have to have that much bump for smooth operation, your die is not a good match for your chamber. There is no adjustment that can solve this. You need a different die.

 

[Coyotefurharvester]

Measure the overall length of a couple of your sized brass. Partially seat a spent primer in each one(about 0.010 proud), you will need to seat them by hand. Chamber the brass, closing the bolt will establish the case head to bolt face clearance. With the shoulder of the case tight in the chamber. If you find +0.004 or more overall length after chambering, you are hitting the shoulders a bit too much for a bolt gun.

 

[K22]

What happens when you oversize the case:
1. Reduces case life.
2. Creates the possibility of case head separation.
3. Does not provide optimum case fit in the chamber for optimum accuracy but not a significant accuracy issue for hunting loads.

The solution:
Get a case head space gauge and learn how to measure fired case headspace and adjust F/L die to provide optimum case fit in the rifle chamber. Only works well if a group of cases are dedicated to a specific rifle and firing / sizing is rotated to produce equal wear of all cases.

 

[Webster]

You need to become familiar with how case head separations happen. There is plenty of information out there on that subject, both on this forum and on the internet. Google is your friend. If you have to have that much bump for smooth operation, your die is not a good match for your chamber. There is no adjustment that can solve this. You need a different die.

What part of the case gets moved back when you bump? For some reason I always assumed the junction of the body and neck never moved. Your taking the bump measurement off of the middle of the shoulder. Seems like it's only the sloping side of the neck that gets moved? Where is the brass moving to when you bump?

 

[BoydAllen]

What part of the case gets moved back when you bump? For some reason I always assumed the junction of the body and neck never moved. Your taking the bump measurement off of the middle of the shoulder. Seems like it's only the sloping side of the neck that gets moved? Where is the brass moving to when you bump?

The shoulder of the case is moved back.

 

[Kracken McGraw]

I used to get some case head separation in a 22-250 Remington 788 action bolt rifle. I think these actions with the lugs on the back were a little suspect to it. Although those days I was setting up my dies per instructions of the Speer manual, looking back now I’m sure I was bumping at least that .007.

 

[M-61]

Fire a round, See if the brass will re chamber with no resistance. If it does, size the neck WITHOUT pushing the shoulder back.
When it starts getting tight to chamber, THEN size the brass being careful NOT to push the shoulder back too far. .002 is a good # to work for.

Exactly

 

[Rob01]

There is no problem with FL sizing every time. You just have to set shoulder for minimum bump. Only neck sizing is fine if you don’t need full reliability and can deal with super tight chambering.

 

[nakneker]

A shoulder bump of .007 is a lot. Even if everything is shooting fine now your increasing your odds of problems with multiple firings. I typically bump between .001-.002 and I typically shoot in a lower node, I’m dialing on most of my hunting rifles any ways and don’t need to squeeze every bit of velocity out of every round.

 

[Doom]

Here we go, technically the shoulder is not actually moved in a classic sense. What creates the growth is the body of the case expands on firing and the shoulder moves relative to the base and reforms as the pressure builds. When the case is resized the body is sized first which pushes the shoulder forward then the die reforms part of the shoulder into the neck and part of the body into the shoulder. The cartridge neck grows and the brass is fed for this from the case body, usually at the base but sometimes higher up on the case. Predominately it is the body diameter growth that creates the majority of the issue.

 

[K22]

There is no problem with FL sizing every time. You just have to set shoulder for minimum bump. Only neck sizing is fine if you don’t need full reliability and can deal with super tight chambering.

I totally agree with this. And I have experience with both neck sizing and full sizing. I stop neck sizing many years ago because of unpredictable functionality problems in the field.

I often set my F/L die for zero to .001" shoulder push back. Cases chamber without issue. Case life is not reduced at all. The reason I believe this works is that when you F/L size, the radial dimension is sized and in my experience this all that is necessary.

The problem with neck sizing is that it doesn't size the radial dimension and more often than not this the culprit in unreliable chambering, at least that has been my experience of loading thousands of rounds for a multiple of rifle brands and calibers.