Case Volume Difference

[mwagn]

I am trying to figure out if I am switching brass from BHA Match to Hornady Match and there is a .3 grain increase in case volume would I just increase my charge weight by .3 grains to keep the same velocity?

 

[mwagn]

The only reason I am concerned about it us that I spent a lot of time and money (components) developing a load that is within the node and I need to keep it there as my wife shoots PRS and would like to be competitive.

 

[Keith Glasscock]

In a word - no.

The good news is this: you likely will still be pretty close or in with your tune. All I’d do is chronograph the new brass to see if/how much velocity changed and adjust the charge to match the old brass. Shouldn’t take more than 10 rounds total.

 

[mwagn]

In a word - no.

The good news is this: you likely will still be pretty close or in with your tune. All I’d do is chronograph the new brass to see if/how much velocity changed and adjust the charge to match the old brass. Shouldn’t take more than 10 rounds total.

Thank you for the information. Since I have to drive to the range to test out ammo I will load up 5 at my current load and then .1 grain increments up to 40.3 and chronograph them

 

[mwagn]

So I bought more Hornady match brass and the head stamp does not say match on it like the other stuff that I have does and the case capacity is Different by 2 grains does anybody have any insight on this

 

[Milo 2.0]

I am trying to figure out if I am switching brass from BHA Match to Hornady Match and there is a .3 grain increase in case volume would I just increase my charge weight by .3 grains to keep the same velocity?

I'd make sure the Hornady brass will handle the original load first. BHA Match some tough stuff.

 

[mwagn]

I'd make sure the Hornady brass will handle the original load first. BHA Match some tough stuff.

I did and it will but I am just going to have to start over with load development

 

[Bart B.]

I've changed charge weights in 308 Win cases about 7/10ths grain for every 10 grains of case weight to maintain good accuracy and minimal average velocity change; less powder as case weight increases. Case weights from 150 to 180 grains involved.

Got that idea years ago from data from someone using an Oehler 35(?) system measuring velocity and pressure across a wide range of case weights.

 

[linedrive301ft]

There is a big difference in the volume between the Hornady Match and the standard Hornady that I have measured.

 

[AP2020]

 

[Bkluke]

Start low and work up to current load. Safety first.

 

[terraMODA]

Using this formula would be a more accurate guestimation. It has worked for me. Velocities were very close!

Charge wt 1 X
—————— x ——————— = gr.
Case cap 1. Case cap 2

If original charge weight is 42 grains and the case capacity is 54 grains h2o, and the new case is 56 grains, then 42x56/54=43.55 grains for new charge weight. Just cross multiply.

 

[2506]

Also take into thought. New case and fired and sized cases usually do not have the same capacity, fired usually has more. Doing load work up with new case then switching to previously fired cases usually screws me up especially with the larger capacity cases.