cartridge pressure versus bullet hardness

[garagist]

Hi Veral, I have a question. When a cartridge pressure is listed in a reloading manual for a given amount of powder,is there any formula available to extrapolate the pressure for a load that is higher or lesser than the load listed? For instance, when 35.000 psi is listed for 25 grains of powder xxx and one wants to load only 20 grains, can you determine with a formula how much the pressure will be approximately? The reason for asking is to find out what the best BNH for the bullet would be with that particular load.

[Harry O]

I'm not Veral, but you might want to get a copy of "Modern Reloading, Second Edition" by Richard Lee and read chapter 9.  There is a relationship, but it depends on the powder.

[garagist]

Harry O, thank you. I have that book but I must have missed it. I will look it up today

[Veral]

  My advise is don't worry about bullet hardness balancing to pressure unless you are having leading problems.

  In my experiance, hard bullets are always best if they fit the gun properly so they prevent blowby before they get burried in the rifling, and hard always gives the lowest pressure with stout loads.  If you have to use undersize bullets and are getting leading with light loads, try a softer alloy until you find how soft they need to be to bump up on the base and seal powder off before the bullet even starts moving.  If using a poor lubricant, this can be a balancing act to find the hardness that just lets the bullet bump up, as too soft will cause leading from obturation pressure/bore friction.