Load Development With New Brass

CalCoyote

CalCoyote

New member
In the days that we are currently living in supplies on primers and powder are limited and who knows when if things will EVER get back to what it used to be. For that reason I do not want to waste powder and primers. With that in mind here is my question:

I have noticed that there are differences in shoulder headspace of new brass. Not as much with premium brass like Lapua or Nosler, but there is still a difference. I was prepping some new Winchester brass for the 243 and found that the shoulder headspace had a variance of approx .006 apart.

How much difference does this variance make in group size?

Can I use new brass for load development or do I need to waste primers and powder to fire them once so that I can bring them all into them same shoulder headspace?

Hopefully this makes sense. I am not too good at explaining things.
 
It will make a difference in group size. A change in length of .006 will make your primers go off different, and it will make your seating depths random. If you have an expander mandrel for .25 or 6.5 cartridge, you could expand the neck, and then set your .243 die up short, and resize your cases so there is just a slight resistance to the bolt closing and do your load development from there. There's also the the Hornady Hydro Sizer that will expand your cases just like fireforming.
 
Originally Posted By: FC363It will make a difference in group size. A change in length of .006 will make your primers go off different, and it will make your seating depths random. If you have an expander mandrel for .25 or 6.5 cartridge, you could expand the neck, and then set your .243 die up short, and resize your cases so there is just a slight resistance to the bolt closing and do your load development from there. There's also the the Hornady Hydro Sizer that will expand your cases just like fireforming.

The odd thing about it was they were NOT all over the board. The .006 difference fell into two distinct groups. Approx 2/3 of the brass were within .001 of each other and the other group was all consistently within .001 of each other but they were .006 less in headspace measurement. It almost seemed like they were using 3 different machines to form the brass and two of the machines were in sync with each other and the third was kicking them out at .006 less. The two groups fell almost perfectly along 2/3 to 1/3.
 
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One of the main purposes of fireforming is to blow the shoulder forward without stretching the brass in front of the web, creating a thin spot that can lead to case head separation. By jamming a bullet in the lands, the case head stays planted against the bolt face so all expansion takes place at the shoulder.
 
Originally Posted By: FC363 A change in length of .006 will make your primers go off different

Now I don’t claim to be an expert but in all my years of reloading I have never heard of brass length affecting the way a primer ignites. Please explain that.
 
I used an old stash of Win 22-250 brass for pd loads this month. They were 0.006-0.008 short for the first firing, I loaded a max load of Varget with a Sierra 55 BK. They shot a cloverleaf one hole group out of a factory Rem varmint barrel(bolt has been bushed and I had put on a Timney trigger). After shooting they still were 0.006 short, just a slight base expansion. I full length sized, with no bump. Loaded more up and they repeated the same groups/poi. Second firing they still don't require any bump and still short by more than 0.002(I checked the chamber with go-no go gage so I can set die by gage). If I had several hundred brass the barrel maybe shot out before the brass is fully formed.
 
Originally Posted By: reb8600Originally Posted By: FC363 A change in length of .006 will make your primers go off different

Now I don’t claim to be an expert but in all my years of reloading I have never heard of brass length affecting the way a primer ignites. Please explain that.

A change in the headspace changes the distance the firing pin travels. Same thing as with flush primers vs very deep seated ones. It doesn't amount to much, but if you have a weak spring it can show on target.
 
I have not seen case head separation from a single firing of new brass that is 0.006,0.008 or more short. It is common for new brass to be that short because of SAAMI specs. Just don't repeatedly size brass short, let it grow only bump when bolt resistance occurs(AR's whole different sizing set-up). For me only a vertical dispersion(stringing) change on targets at maximum expected shooting distance would be proof of a primer induced change. Your primers should always be below the brass face(no proud primers), firing pin protrusion is usually in the 0.055-0.062 range so 0.005-0.006 short brass seems statistically insignificant as far as the primers performance.
 
Why bother doing anything then? Just shoot it and be over it. It's a .243 field rifle. It won't know the difference anyway.
 
Exactly with today's components market/price why chase .1-.2's with anything other than competition benchrest equipment. No need to fire form factory brass to a factory chamber. If its a field(hunting rifle) load hunting ammo.
 
Originally Posted By: FC363Originally Posted By: reb8600Originally Posted By: FC363 A change in length of .006 will make your primers go off different

Now I don’t claim to be an expert but in all my years of reloading I have never heard of brass length affecting the way a primer ignites. Please explain that.

A change in the headspace changes the distance the firing pin travels. Same thing as with flush primers vs very deep seated ones. It doesn't amount to much, but if you have a weak spring it can show on target.

Well, you believe what you want. The only thing that MIGHT affect is if it fires at all. Not going to make one fire more than another.
 
SAAMI ammunition primer specs 0.000-0.008 below face, combine with ammunition often 0.008 short of bolt face to cartridge base. You easily can have a stacked tolerance of 0.016 or more(if primer not fully seated in primer pocket and the firing pin strike pushes in). I like the primer pocket to be 0.002-0.004 deeper than the primer cup height. Than I seat the primer bottomed out to 0.001-0.002 crush. It is very common to have primer movement in the pocket either before primer ignition or after(primer pushed out to bolt face).
 
.006 is not much to worry about. I have seen .012 variance.

Things that do matter are:

tuning the load with a particular distance from the lands

Primer choice

powder choice

243's are usually easy to load for. I do bed the rifle, free float the barrel, tune the trigger before I ever pull the trigger.

60g Sierra with AA2700 and Win 760

80g Sierra, Nosler BT, Berger 80g with IMR 4064 are money in the bank when it comes to accuracy!
 
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