Thread: Is it Pressure or Powder Capacity?

Originally Posted by grandpamac

Greetings Hermitage,
I had a quick dig on the internet and came up with a couple of barrel life calculators including Mikes Spreadsheet. The input variables for the calculators are:
Projectile diameter.
Powder charge weight.
Powder heat potential.
Pressure.
Projectile coating if any.

The powder charge and heat potential determine the amount of heat available. The pressure determines the way the heat is applied to the throat and the projectile diameter determines how much steel that heat is applied to. So rather than pressure alone driving erosion it is a number of factors. If pressure only was the culprit then the .243 and .308 would have the same life, or .25-06 and .270 for that matter. This is definitely not the case.
Regards Grandpamac.

Oh, I realise pressure is not the 'only' culprit....that it's intuitively expected that there are a number of factors all interconnected. But I still feel it is the #1 cause of barrel erosion if the culprits are to be ranked.
Actually, I suppose if I was to make a simplified list of 'culprits', I would expect erosion to be caused by heat (which is increased by pressure) versus time (more case capacity = more burning time) versus pressure build up. But I can't be 100% sure about my theory.

I also had a quick look on the internet and didn't realise the topic of barrel erosion was so complicated....just look at the below which I read on causes of chemical and thermal barrel erosion:

"Consider the definition of impetus, I, used to gauge the propulsive energy provided by a propellant,
I = RTf = RTf /M, (10)
where R is the specific gas constant, R is the universal (molar) gas constant, Tf is the propellant flame temperature,
and M is the molecular weight of the propellant gas mixture".