Case thickness and pressure

[jsthntn247]

I've got win and RWS cases for my 300 win. The RWS cases average 4 grains less water capacity(92.35 to 88.3). Does this mean I will see the same pressure with 4 grains less powder in the RWS cases?

 

[sharpshooterbr]

Not necessarily, the smaller case volume will raise pressure, but it might not be an exact correlation to the water capacity difference. You should work up loads with each type of brass individually to make sure you do not hit pressure.

 

[BuzzBoss915]

Yes, good reply. It's not a linear number, four grains equals four grains anyway. I have never used RWS, but some people report resizing problems because of the wall thickness, something about spring back?

But, here's the thing. You must separate your cases by headstamp and work up a load for each brand. At least you know, and are aware of the different case capacity, but that COULD indicate using a completely different propellant and bullet. Four grains difference in capacity is significant. BB

 

[Twoboxer]

. . . The RWS cases average 4 grains less water capacity(92.35 to 88.3). Does this mean I will see the same pressure with 4 grains less powder in the RWS cases?

No. All else being equal, pressure is inversely proportional to volume. You have measured a volume difference of (92.35-88.3)/92.35 or 4.4%. So I think it means using the RWS cases, with all other variables held constant, you will see ~4.4% more pressure than in the WIN cases. If your powder charge was 50gr, a ~2gr reduction might likely be right.