Thread: Chamber pressure, expansion ratios and muzzle pressure

Well the title says it really

In the old guns world we talk about chamber pressures a lot because certain actions are suitable for this or that chamber pressures in their original configuration.

Then we muddied the water with that new fangled smokeless powder ( it will never catch on ).

But we don't see much about powder expansion ratios and pressures at the muzzle when the bullet exits ?
Or do you smart tech guys have that on tap with internal ballistic programs ?

Why would I be interested in muzzle pressures ?
I am contemplating a very challenging barrel bore and line project for myself.
I have all the data sheets from the European "Individual Proof Of Weapons " ( a mine of info on minimum chamber wall, minimum barrel wall and extractor cut out maximums ) and can make the numbers for chamber and bore minimums easily until I am 1/3 along the barrel and then I would want to step my liner diameter down in two stages.
My rational is that chamber pressure is a very brief moment in time and that internal pressures reduce significantly towards the muzzle.
But with progressive nitro powders the powder expansion ratio is a key factor in pressure at the muzzle

Does anyone have any authoritative information on this subject ?

I do know what I am doing and I haven't blown one of my bore and lines up yet.
I do not include the original bored out barrel in my hoop strength calculations and in this case it will only be 1.25mm anyway

Hopefully this makes sense to someone