Headspace variance- now what?

[marchx]

I have a batch of 2 times fired Lapua brass in 6BR. I deprimed all the cases, cleaned them in ultrasonic cleaner and dried. I annealed the brass using induction annealer up to the point of Tempilaq 750 changing colour.

Now:

I FL sized the brass using Forster FL benchrest die (I pulled out the expander ball though), imperial sizing wax. The FL die was set to give 3 thau shoulder bump (based on test case).

I ended up with my brass being divided in 3 separate groups:

60% of brass has the desired 3 thau shoulder bump

20% of brass has 4 thau shoulder bump

20% of brass has 5 thau shoulder bump

The brass was previously sorted based on weight and trimmed to length.

The question is: how should I proceed from now on? Should I use for competition only group no. 1, disregard groups 2 and 3?

 

[jelenko]

Interesting. I usually get +/- 1 thousanth spread but with most of it in the 'middle'.

 

[Bill Norris]

Following

 

[Bc'z]

Grab a index card..
Now throw some calipers on it..
Does it measure .007??
So we're talking about something less than the thicknesses of a index card, Hmmmmm?
I think I'd load and shoot it, but thats just me.

 

[Chaotik]

All within .002.
I usually don't sort unless there is a greater variation, but is that typical variance for your sizing die?

 

[DJSBRS]

This issue is not uncommon as there are several things that causes your dilemma. The main issue is the brass did not accept the annealing to the necessary point of being relaxed. Some brass must be reannealed several times to conform to your die setting. Additionally, a build up of sizing wax will form inside your die and cause a variance in case headspace pressure. Just the viscosity of the lube on the case must be the same to obtain consistent cartridge reforming.

DJ

DJ's Brass Service

 

[nwmnbowhunter]

At the end of your stroke, when sizing, hold pressure for 5 seconds. See if this gives the brass a chance to set, and give you tighter variance. Worked for me

 

[mikecr]

Or you could try no annealing at all.
That is, once you've worked the cases back to consistent & useful hardness.

 

[marchx]

@DJSBRS @nwmnbowhunter
1. Yes, I expect the brass to be underannealed. So, practically not annealed.
2. I let the brass sit for 4 s in the FL die.
3. Good point on build up of sizing wax, will have to consider this next time.

Would you guys consider only group no. 1 as fit for competition, or group np. 1 and no. 2 combine would do just fine during a match (1 thau variance)?

 

[marchx]

Or you could try no annealing at all.
That is, once you've worked the cases back to consistent & useful hardness.

I don't know what that means. I am a rookie in this department.

 

[Bc'z]

I don't know what that means. I am a rookie in this department.

Grab a .005 feeler gauge and look at the edge of feeler gage.
This is what your stressing over, just saying.
Now load 3 from your batch with .005 bump, and 3 from your .002 bump.
Mix all 6 rounds up for a blind test and shoot them, then tell us what you see.

 

[rr1220]

Were all cases fired with the same charge weight

 

[mikecr]

Fire your new brass a few times to fully stable with no body sizing or annealing, and test to see what you should be bumping from. Then see how well it takes your correctly set bump.
It could be that you never need to anneal the shoulders.

 

[Link]

I have a batch of 2 times fired Lapua brass in 6BR. I deprimed all the cases, cleaned them in ultrasonic cleaner and dried. I annealed the brass using induction annealer up to the point of Tempilaq 750 changing colour.

Now:

I FL sized the brass using Forster FL benchrest die (I pulled out the expander ball though), imperial sizing wax. The FL die was set to give 3 thau shoulder bump (based on test case).

I ended up with my brass being divided in 3 separate groups:

60% of brass has the desired 3 thau shoulder bump

20% of brass has 4 thau shoulder bump

20% of brass has 5 thau shoulder bump

The brass was previously sorted based on weight and trimmed to length.

The question is: how should I proceed from now on? Should I use for competition only group no. 1, disregard groups 2 and 3?

2 firings - is this brass fireformed to your chamber yet?

 

[marchx]

Were all cases fired with the same charge weight

Yes, Sir.

 

[marchx]

@marchx I realized my response sounded kinda harsh, I realize your wanting to figure out whats causing the variations.
My 1st thought was the amount of lube that could be building in the die with every piece sized, it could also be a dirty shell holder. Dirty shell holders can also induce runout.
Now to your concern about shooting said brass in a match. I would, and not give it a second thought.
You should have enough tolerance built into your load to cover charge weight and seating.
Now your brass that's sized .005 is only .0035 different from your brass with .0015 variation.
Hopefully this helps you see things a lil more clearly.

I was thinking again about the amount of lube. I don't think it's likely to be the main cause of the problem- I was distributing imperial wax using q-tip in a consistent way over the case. Before sizing I cleaned the die. So, how much wax could build up after sizing 10 cases (my whole batch is 30 cases)?
No shellholder- I am using Co-ax.

 

[marchx]

2 firings - is this brass fireformed to your chamber yet?

Forgive me my ignorance, but why should this matter? Regardless of fireformed fully or not, I am FL sizing the brass, so a case should be brought back to predefined dimensions. Moroever, after 2 firings the cases should have the same dimensions- they were fired in the same chamber using the same charge weight.

 

[marchx]

Fire your new brass a few times to fully stable with no body sizing or annealing, and test to see what you should be bumping from. Then see how well it takes your correctly set bump.
It could be that you never need to anneal the shoulders.

I think it's safe to assume I underannealed the brass. I think the exercise you suggest would answer another question- how much bump do I need given my chamber. The question I would like to answer is however different- regardless of how much bump I choose, I need the shoulders to be bumped in a consistent way, showing no more than 1thau of variance, ideally zero variance.

 

[marchx]

I suppose cleaning the die with brake cleaner or isopropyl alcohol and sizing a piece of brass could answer that question.
I've never used a Coax press. How much movement is there to the die block where die is located?

 

[snert]

In regard to it being fully formed in two firings...sometimes yes, sometimes it takes more. I think that is what the person who answered was getting at. I prfer a solid three firings before I am convinced it has stabalized and is actually formed to my chamber. More in some wildcat cases, especially shortened ones from thick brass (but that isn't your case). In the end, I agree with those that have suggested it won't make a difference...shoot em!