fire formed brass

[SSN Vet]

Hey guys,

I neck size for my only bolt action rifle (7mm-08) with the Lee collet die, so that's all I really know.

But I recently loaded cases purchased new, which I neck sized and uniformed the primer pocket, and then loaded same as my fire formed brass.

I loaded the 140 gr. SGK BTSP in the fire formed brass

and the 139 gr. Hornady BTSP in the new brass.

Both were loaded with the same charge of IMR4350.

I was surprised to see that the SGK loads gave much better results.

I would have figured these two bullets were pretty much the same, so I'm wondering if the improvement was do to the brass being fire formed (I can definitely tell the difference when closing the bolt).

Inquiring minds want to know

 

[Archie]

"... gave much better results." Better accuracy or greater velocity? Or both?

Too many variables to give a good answer.

It could be the SKG bullets respond to that loading better.

Or it could be the non fire-formed brass (which is now fire-formed, by the way) expanded to fit the chamber, and in doing so used up some of the energy that was not used to push the bullets down range.

Or it could be the non fire-formed brass allowed the case to move (microscopically) in the chamber, resulting in a decrease in accuracy.

Could be the fire-formed brass was heavier on average than the 'new' brass. Being heavier means the inner volume is smaller (the extra brass has to be somewhere) and a smaller volume would result in greater pressure.

Try this again, but limit the other variables as much as possible.

 

[witchhunter]

The only way to tell would be to load the same bullet in both cases and redo your test. Only change one item at a time.

 

[SSN Vet]

The only way to tell would be to load the same bullet in both cases and redo your test. Only change one item at a time.

I understand that... which is why I was hoping someone else who had done more extensive, controlled testing would chime in and share their opinion on the topic.

 

[Snyper]

Any time you change one of the variables, accuracy can also change.
Knowing exactly "why" one gun prefers one load over another isn't always possible.
Just be happy you found a load that works, and try to duplicate that in the future

 

[Reloadron]

The only way to tell would be to load the same bullet in both cases and redo your test. Only change one item at a time.

That is also the corner I am in. I just loaded some .308 Winchester with the same bullet (150 gn SMK) but using Remington new brass and some LC 13 GI brass. Different chronograph readings and different point of impact on a 100 yard NRA small bore rifle target. The loads were identical and the only variable was the brass.

I suggest loading either or both empty brass using both bullets and the same load. When I do load development I try to only change a single variable at a time, right down to the primers.

Additionally sooner or later you will likely need to full length size your brass, neck sizing only works so many times. Eventually the bolt will be harder and harder to close with each reloading until they no longer chamber. That would be my guess anyway.

Ron