Is there a formula to adjust loads based on case capacity?

[ratbuster]

If you are switching case brands that have less case capacity (say .5 grains of water on average) is there a good way to approximate how much to reduce the charge to start out? I realize you could always go back to a starting load but to be more efficient there has to be a way to calculate a charge that is close to the original load and from there back off somewhere in the rage of 2-5% instead of the usual 10%, depending on how hot the original load is to start with. Any ideas?

 

[Sheldon N]

A good starting point would be that a 1% change in case capacity is equivalent to roughly a 0.5% change in velocity.

For example with a 308 case losing a half grain of H2O capacity is about a 1% change, so you'd want a corresponding 0.5% reduction in powder charge. If you had a 43.5g load, that would now be a 43.3g load. With a bigger or smaller case the percentages would be different.

 

[Catfish]

It would depend on if your first load was a max. load or a lighter load, and how full your case is. If you are compressing your charge in the first case and have no pressure signs you need only back down to a non compressed load. If your using a fast powder and filling the case to 1/3 full, start all over.

 

[savagedasher]

A good starting point would be that a 1% change in case capacity is equivalent to roughly a 0.5% change in velocity.

For example with a 308 case losing a half grain of H2O capacity is about a 1% change, so you'd want a corresponding 0.5% reduction in powder charge. If you had a 43.5g load, that would now be a 43.3g load. With a bigger or smaller case the percentages would be different.

That's the numbers I use .02 h20 to .01 of powder . Larry