I am surprised you are stating your position based on what one person told you over the phone."
Where did I say i took a position based on one phone call?
"keep an open mind and research this"
That's exactly what I'm trying to do! And I do appreciate the other posters viewpoints.
And er, uh, maybe ya 'll need to open your minds.
Messenger boy here, don't kill the messenger!
From friend, ballistician, chemistry major and very well known writer. His email answer to me,
one of many from labs which pretty much all said the same.
"They don't all burn up within 2". The peak of the pressure curve will vary, say from 1/2" in front of the chamber in a .45 ACP with 10 grains of a very fast-burning powder to maybe 3-4" in something like a .30-378 with 100+ of very slow powder. But the powder does essentially all burn up just in front of the case. The peak of the pressure curve is where it is all burned up.
....with a couple of caveats. The peak pressure developed must be in the range that the powder's designed for. For instance, IMR4895 works very well in the .45-70 at low pressures for trapdoor Springfield loads, but in that case it's only developing 25,000 psi, not the 50,000 psi IMR4895 is designed to burn at most effectively. But the powder doesn't keep burning on down the bore. Some of it simply doesn't burn, and if you place a sheet on the ground in front of the rifle you'll find unburned powder granules all over the place.
Even at the correct pressure a tiny bit of powder doesn't burn, 1% or less. But again, it simply isn't going to burn. All the powder that WILL burn is burned up just in front of the chamber.
So no, different powders don't ALL burn up within the exact same distance in front of the case. The cartridge, powder, bullet all have an effect, and the point of peak pressure does vary. But the powder doesn't keep burning on down the bore. The gas created keeps expanding.
All of this was proven many years ago by Homer Powley during his work at goverment arsenals."