IceAxe wrote:I believe the graph that Hoot posted shows peak pressure not propellant burned. Here is a printout that shows an idea of percent of a powders burn.
IceAxe-
Thanks for posting the QuickLoad printout. I'll assume you were responding to my post immediately preceding yours.
I tried to qualify my statement about powder burning by stating that the pressure curve shows the
effects of the powder burning. I did not mean to imply that all the powder had been consumed when pressure peaked.
I did err in not similarly qualifying my statement: "All of the powder that is going to burn will burn in the first very few inches of the barrel." I should have written "
Almost all of the powder..."
Here's a QuickLoad graph that was posted on the Firing Line forum on a 2013 thread:
Powder Burn in Chamber or Bore?.
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I have edited the graph for smaller width, and added the Blue Arrows. For this cartridge with the stated load, the left-hand blue arrow shows that 80 percent of the powder is burnt in the first four inches of the barrel, and the right-hand arrow shows 90 percent burnt in the first seven inches. About 60 percent of the powder is burnt at the point of max pressure, when the bullet has moved about two inches. Hoot's graph shows the peak pressure at one inch for the Bushmaster, with the differences due to the powders and cartridges.
It's likely that the burning of the last 10% of the powder contributes negligibly to an increase in pressure and velocity, because the volume of the chamber and bore have increased substantially. So, the burning of the final 10% of the powder is going to raise the pressure behind the bullet comparatively little, with relatively small resulting increases in velocity.
All of the above is from my reading and correspondence, since beyond inpection of fired cases for gross signs of pressure, I've collected no pressure data myself. However, it does pretty much match what I've seen.
Thanks again.
--Bob