Velocity difference between new brass and fired brass

[milo-2]

There is always some difference, and much of it depends on how sloppy your chamber clearances are. Given this, you should not count on or develop a load with brass until it's fire formed.

This is how it goes down; new brass expands on first firing, absorbing some of the pressure peak.
With that first firing, and a couple to follow, the brass is forever changed.
Subsequent pressure peaks are different, and higher when chamber clearances are less (and less absorbing).
When you change brands or even lots of same brand, it affects your load's peak pressure & timing.

Ideally, your reloading plan would not endure this issue.

You put 3-500 pcs of brass into service for one rifle, like myself and most of my friends do, it does not make much sense to not develop on new brass.
With a small amount of common sense, I've weathered both barrel speed ups and once fired brass on loads w/o a hitch. No, it is not always that way, but can be done.

 

[Mikecr]

We all have different standards that we accept.
But whether 50pcs or 500, practical or not, the tune is not stable until the cases are stable.

 

[milo-2]

We all have different standards that we accept.
But whether 50pcs or 500, practical or not, the tune is not stable until the cases are stable.

Either way, you make it sound like pulling or adding .1-.2gr an issue. Size and prep 10 pcs of brass and test them, before doing them all. A variance in neck tension may be needed. I never implied jumping blindly into anything.

 

[Mikecr]

OK, you size & prep 10pcs and fire them let's say~4 times each with a load development. Now you have a good load and 10 developed cases it applies to. This means what for the other 490, which you intend to fire form -eventually?
Are you then going to develop a load for new brass, using ~40cases, so that you can use 450 with 1st fire forming?
Then do it again for 2nd fire forming?
Are you suggesting that there is so little difference between new brass and fully fire formed brass(for you) that it doesn't matter?
And are you saying that it just isn't viable to fire form 500pcs of brass up front, because it would wipe out your in barrel doing so?
I agree with the last, and am glad I don't need to develop 500 cases.

I'm pretty sure your situation is kind of specialized, and that by far most people do not need so many developed cases.
Personally, I've never needed more than 50 on-hand. And with this, I go ahead and fire them to fully stable before moving to powder development. During this fire forming I would do primer testing, and full seating testing, and 'MyMax' load testing only.
With my cartridges, and charging for full load density and near SAAMI max pressures, where I get best results, there is significant difference between new and developed cases. So much so that it makes no sense to **** with powder while cases are still changing.
And for sure I don't use cases still changing for hunting or competition.

If I needed 500 cases, let's say for PD hunting, then I would have a scrap fire forming barrel chambered along with my hunting barrel to handle this. Spend a week developing my brass, and then move into powder development with my hunting barrel.
Less tail chasing.

 

[milo-2]

OK, you size & prep 10pcs and fire them let's say~4 times each with a load development. Now you have a good load and 10 developed cases it applies to. This means what for the other 490, which you intend to fire form -eventually?
Are you then going to develop a load for new brass, using ~40cases, so that you can use 450 with 1st fire forming?
Then do it again for 2nd fire forming?
Are you suggesting that there is so little difference between new brass and fully fire formed brass(for you) that it doesn't matter?
And are you saying that it just isn't viable to fire form 500pcs of brass up front, because it would wipe out your in barrel doing so?
I agree with the last, and am glad I don't need to develop 500 cases.

I'm pretty sure your situation is kind of specialized, and that by far most people do not need so many developed cases.
Personally, I've never needed more than 50 on-hand. And with this, I go ahead and fire them to fully stable before moving to powder development. During this fire forming I would do primer testing, and full seating testing, and 'MyMax' load testing only.
With my cartridges, and charging for full load density and near SAAMI max pressures, where I get best results, there is significant difference between new and developed cases. So much so that it makes no sense to **** with powder while cases are still changing.
And for sure I don't use cases still changing for hunting or competition.

If I needed 500 cases, let's say for PD hunting, then I would have a scrap fire forming barrel chambered along with my hunting barrel to handle this. Spend a week developing my brass, and then move into powder development with my hunting barrel.
Less tail chasing.

Like you said earlier in the post, chamber size a big factor. And no, I just fire new brass for a suitable load, then fire it all. When time to process, I start with 10 first, it is simple, if all is well, proceed, if not, make changes.
I couldn't fathom having only 50 pcs of brass for any rifle. I fire all brass, process, never is my brass count off on number of firings. If my brass is in the process stage and I need to shoot, I grab a rifle that has brass ready to load.