Thread: Sako Brass

Greetings All,
There have been a few myths about regarding increased case capacity and velocity. Some have claimed stupendous increases in velocity due to changes in case shape and hence capacity but actual pressure tested results have shown these increases have only been gained with stupendous increases in pressure. A few years back John Barsness developed some rules relating to case capacity and velocity based on pressure tested load data. One rule was that possible velocity increases at 25% of the increase of available case capacity. I used this rule, when developing some loads in my 6.5 x 55, to calculate what velocities should be possible and it worked well.
Using the .308w as an example case weights vary from about 170 to 190 grains including the fired primer. 20 grains of brass work out to about 2.3 grains of water or 2.2 grains of powder or a 4 to 5% increase. This works out to 1 to 1.25% increase in velocity or around 30 fps or about what you would get from an extra inch of barrel. Worth thinking about.
Regards Grandpamac.