Hi Guys....

I am curious.  Has anyone sort of 'mapped' the relationship between case weights and pressures?

I'm running a 280 Ackley Improved, and with a full charge of RL22 I can get 160 Nosler Partitions running at just a smidgen over 3000 fps.  This is using fire formed Norma 280 Rem brass.  The load is just under Nosler's max load, and its fully safe and showing no signs of excess pressure in my rifle...

I just loaded a bunch more Norma 280 Rem cases with my fire forming load.  Before loading I spot checked ten cases.  Average case weight is running 193.1 grains....  I finally managed to buy some actual Hornady 280 AI cases.  These are running an average of 178.4 grains....

As much as I can figure, the lighter Hornady cases should run the same load with a bit less pressure, and therefore a bit less velocity.  Same external dimensions, and lighter case weight mean that there is more internal capacity.  More capacity means less pressure.

Anyone running a similar pressure cartridge seeing an actually observable velocity change switching from one case make to another, given this 15 grains or so case weight difference?

thanks

Fro

Case weight can be misleading. Always measure case capacity.

They say the average ratio is 8 to 1 meaning 8 grains of case weight equals 1 grain  of power capacity. But this doesn't mean a difference in pressure equal to a charge weight change of the same amount. In fact that could not be farther from the truth.

Theoretically your assumptions should be correct in lighter case will equal less pressure with a given powder charge but you may be surprised at how little difference it makes.

When you notice it the most is when you are already pushing the envelope and happen into casings with less capacity. So reverse your current situation. Say you worked up to a maximum load using the lighter brass then tried the same load in the heavier brass you very likely would see some signs of more pressure like flatter primers and maybe even sticky extraction or more effort to open the bolt.

Motor

Did RocketmanOU do this?