Velocity difference between new brass and fired brass

[david g ranes]

What do you feel the average difference in velocity you are getting between new brass and once or more fired brass of the same brand and is it enough to goof up your velocity on your ballistic turret at distance I seem to be getting quite a difference. David

 

[milo-2]

In my experience, it varies so much from chamber to chamber and brass composition between brands. To me Norma brass has been forgiving where I don't see much change, and older Lapua brass used to seem the same. Using newer Lapua brass today I seem to get a 10-15fps increase, same load, on once fired brass, but it could be chamber size also. Other than my 7 saum, which I shoot Rem brand brass, Lapua is all I am firing at the moment.
On a 3000 fps rd, 30 feet more per second is a 1% increase, not much in the grand scheme.
I should add, i am always prepared to pull .1-.2gr of powder on fired brass.

 

[david g ranes]

I got 40 ft per second difference between new Hornady brass versus fired brass on my 6mm Remington not much to choose from on brass got tired of waiting on Winchester and Remington brass. David

 

[milo-2]

I got 40 ft per second difference between new Hornady brass versus fired brass on my 6mm Remington not much to choose from on brass got tired of waiting on Winchester and Remington brass. David

40 fps seems excessive to me, and I am not going to badmouth the brand, but if your load went out of whack, pulling some powder should get it back into your former pressure range it liked.

 

[JMW67]

I got 40 ft per second difference between new Hornady brass versus fired brass on my 6mm Remington not much to choose from on brass got tired of waiting on Winchester and Remington brass. David

What we have been doing for 6mm brass is using norma 7x57 sizing to 257 Roberts then to 6mm and turning necks much better than any 6mm we could buy usually 7 to 8 firings and we run them pretty hot

 

[david g ranes]

Thanks

 

[Gwine]

On my last new brass I did a little experiment while fire forming. 7mm08 starline brass. After finding pressure and a decent node I loaded 30 doing nothing more than running an expander through the neck for uniform necks. (same as I did to the ladder loads) I full length sized the next 50 brass before loading. With the same load I was 25fps slower. Once all brass was fire formed, the same load gave 8fps faster than the virgin.
All with same powder charge.
-fire formed-2638
-virgin new unsized-2630
-new full length sized-2605
I did adjust most loads to be at the node 2630.
Aprox 41g+/- IMR 4064, 162a-max, cci lrp, all jammed .010

 

[Mikecr]

What do you feel the average difference in velocity you are getting between new brass and once or more fired brass of the same brand and is it enough to goof up your velocity on your ballistic turret at distance I seem to be getting quite a difference.

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.

 

[J E Custom]

What do you feel the average difference in velocity you are getting between new brass and once or more fired brass of the same brand and is it enough to goof up your velocity on your ballistic turret at distance I seem to be getting quite a difference. David

The factory brass is undersized so it will fit in any chamber. you might volume test the new case and then test the fired case when it has been sized like you like it. normally the smaller the case capacity the higher the pressure and velocity with the same primer and powder charge,

J E CUSTOM

 

[243winxb]

Case volume is 4% difference on the little 223 case. New vs fired. Gov. test.

 

[Mikecr]

Normal variances in capacities (within same lots) affects SD. Big capacity changes, like with brand changes, might as well mean start over.
Variances in brass expansion affects tune. And the expansion energies here change when brass undergoes up/down sizing cycles.

Seems like ~5yrs ago, a new shooter showed up at Williamsport (1Kyd IBS) with new brass in 6BR. His first 10shts in competition put 9 of them inside 1 inch! Williamsport is unique in that their format calls for 10sht groups.
When this was reported, there were quite a few others who declared seeing similar with new brass, and there was a lot of great discussion about it.

The important learning in this is that nobody can reproduce it -with that brass -once it's been fired.
No sizing plan can undo the changes occurring with a firing of brass, and there is no way to predict or match expansion energies with unfired brass. So results of this situation will always manifest as random.
That's why it's important to directly fire form brass to stable -before beginning with load development.

 

[RT2506]

Don't know about the velocity difference because this was before I got a chronograph. Back in the early 1990s I bought a new Rem 700 stainless in 7mm Rem. mag. I started with new Rem. cases. I ran them through the sizing die to uniform necks. I started my load work up using AA3100 and 139 Hornady Interlocks to be used on bean field deer in east NC. I could not find a load that would be much under 2 inches at 100 yards. I thought I had a lemon because I had glass bed and free floated barrel and adjusted trigger down to 2 1/2 lbs. The last try at load development I used up all the new cases. I then just partial sized, "neck sized" using a full length size die and loaded up what had been the best previous load to give just one more try before sending this rifle down the road. First shot was on paper. Shot second shot and could not find another shot on the paper while looking through the spotting scope. Thought, great, now it won't even put two shots on a target. Shot my third shot. Same result. Shot my fourth shot and when I looked through the spotting scope there was still only one hole in the target but it looked a little bigger than before. I carefully fired the fifth shot and that hole looked just a little larger. When I retrieved the target all five shots had gone into a hole about the size of a 30 cal bullet hole. Turned out that if you just part sized a previously fired case you could just about fill the case up to the start of the neck with AA3100 and load any bullet from 160 down to 139 gr and it would shoot sub MOA. So you will never know the results in YOUR rifle until you try them.

 

[waveslayer]

What do you feel the average difference in velocity you are getting between new brass and once or more fired brass of the same brand and is it enough to goof up your velocity on your ballistic turret at distance I seem to be getting quite a difference. David

You will need to chrono your different brass. To answer your question it is from the brass expanding to your chamber. So more volume with the once fired brass. I know for some calibers I need to reduce my load by as much as .5 grains of powder compared to once fired brass. That is very normal.

 

[Mikecr]

Normal is actually opposite of that.
Say you work up a load with new/unfired cases to a near max. Those cases represent lowest capacity for charge (from that brass) so it's easy to assume that with the load more confined pressure will be higher. But that is a static notion rather than a dynamic reality.
If you are neck sizing only to reload those cases (now fired), and using that same 'near max' charge, you will see an increase in MV, and likely some pressure signs/problems.

Why is that? the fired & neck sized only case now represents larger volume for charge, and lower load density due to lower confinement, so the pressure should have dropped. But it doesn't. It goes up.
The reason is that confinement here is dynamic across time, either as cases expand,, or as case expansion is prevented (by the chamber).
Then add that powder burn rate is affected by this confinement in a way so nonlinear that it cannot even be credibly considered in a static sense.