case differences = muzzle velocity differences

[Steve]

Ok, I thought I understood, but now I'm confused.
Alright, here we go.
I understand that with thicker cases and less H2O capacity you have to watch out for pressure, but here's my question.

Why would a,new lot) Lapua brass case with the same water capacity but just heavier brass in weight than Winchester cause the bullet with the same weight bullet, same load of powder behind it seated the same OAL to be slower in muzzle velocity?

 

[kelbro]

Shouldn't that be 'measure after firing and before resizing'? Chamber volume minus the space that the brass occupies?

 

[Steve]

What I am talking about is taking either new of each or full length resized of each or just neck sized of each, load them up exactly the same and you will get different velocities between brands of cases, new lapuas versus new winchesters, etc...all being fired from the same gun

If all things being equal ie case volume, powder charge, seating depth, primer, and bullet weight, why would lapuas be up to 100 fps slower than winchester brass?
Is it the pressure spike being different causing burn of powder to be different effecting velocity?

Now granted if case capacity was different then yes I understand pressures would be different and you have to watch for pressure signs from one pet load of x brand brass to the different brand different case volume brass.

 

[kelbro]

Your editing of your earlier post really makes this post appear fragmented and it no longer makes sense.

Simply put...

Different headstamps:

same empty weight AND same water volume = same pressure

different empty weight OR different water volume = different pressure

As mentioned in my earlier post, the difference lies in the difference of the 'net' chamber volume.

 

[CPorter]

Case weight and volume aren't the only things that can affect pressure.

Different cases are made with different levels of copper and zinc which affects the yield strength. There are also other impurities like lead and iron that affect yield strength.

C2600 brass specs
Copper 68.5 - 71.5
Iron 0.05 max
Lead 0.07 max
Remainder Each Zn


I'm sure the different manufacturers anneal the brass slightly differently and maybe at different times which will also affect yield strength. Lapua brass appears to be annealed as a final stage so it will have a lower velocity than one that isn't.

Case weight and volume aren't the only things that can affect pressure

 

[Steve]

kelbro, I don't see how it appears edited or fragmented, clarified maybe.

Thanks CPorter that makes sense to me now, different expansion rates of different brands of brass with same reloading criteria effecting pressure and velocity.

 

[kelbro]

kelbro, I don't see how it appears edited or fragmented, clarified maybe.

Thanks CPorter that makes sense to me now, different expansion rates of different brands of brass with same reloading criteria effecting pressure and velocity.

I guess that I should have 'quoted' your first post, with your question, then my reply would have made sense. As you left it, my post was a response to a question that you removed. Oh well...

I will still stand by my statement. I have fired literally tens of thousands of rounds of 223 and collected the data over several years. I have performed many tests including mixed batches of headstamps that are of the same weight and volume. That mixed lot includes military and commercial brass from around the world. Once it has been fireformed to the chamber, the expansion properties of the brass are negligible. It performs for all intents and purposes, the same.

 

[mikecr]

Steve, have you measured H2O capacity of the fireformed cases?

If fireformed brass is producing 100fps lower velocity with all else equal, it has higher capacity or the flash hole is a different size, or both.
The brass weight doesn't really matter.