I think Mr. Sisk was referring to peak pressure. To get the same velocity the average pressure would need to be nearly the same assuming the average drag on/friction between the bullet and the barrel was close.
I’m pretty sure that Mr Sisk is more knowledgable on this subject than me, especially the friction on clean vs fouled barrel.
But acceleration is directly related to pressure pushing minus the drag. With area and mass being part of the equation.

Edit: Oops, I see that Charlie answered before I got my two cents in.

Last edited by Bugger; 03/06/24.
I prefer classic.
Semper Fi
I used to run with the hare. Now I'm envious of the tortoise and I do my own stunts but rarely intentionally