Here's another place where the S/W Program Quick-Load can answer questions for the Internal-Ballistically challenged (or just the curious), by presenting graphs and numbers that attempt to model the process.
I plugged in a generic .300 Win mag, 24 inch barrel, COAL=3.340"
and Nosler #4 book-safe load of 75grs RL-22.
Even though the barrel is 24 inches long, that includes the chamber, so the bullet actually starts at about the 3 inch point. The peak pressure occurs just about the time the bullet clears the case mouth (ie: has moved only .6 inches forward ... its seated depth).
Barrel position " - Psi (rounded) -- % of powder burnt by this position -- Velocity
3.5--- 61K -- 52 -- like a snail
5 --- 60 K -- 57 -- 1400
10--- 38 K -- 86 -- 2200
15--- 26 K -- 95 -- 2650
20--- 19 K -- 98 -- 2900
24--- 15 K -- 99 -- 3050
As you can see, with 95% of the powder burnt by the time the bullet has reached the 15 inch point in the barrels length, most of the additional velocity gained is from the existing pressure (behind the bullet), not from the last couple percent of unburned powder being burned. Hope this helps visualize it ..
... Silver Bullet
