prm, the plot reminds me of one I saw years ago in an NRA book. Having bullet motion and pressure on one time plot makes analysis much simpler, as you have pointed out. Being the plot of simulation results, it won't settle the question.
You mention the pressure did not halve. I'll note that if gas production ceases with peak pressure and if the volume has doubled after the peak, then the pressure should not be about 1/2 the peak, but instead should be around 40% of the peak.
When gases expand against a piston, they are doing work against it and transferring energy to it. This energy transfer causes pressure to drop faster than application of the basic gas law would suggest, which is the halving you mention. Instead, the pressure drops roughly according to this formula:
pressure ratio = (volume ratio) ^ k
where k is about 1.25 for propellant gases. For a doubling of volume, this represents about a 60% drop in pressure. Further, heat losses to the barrel and chamber accelerate this ideal pressure drop.
This is why I've been harping about the shape of all the pressure traces; they simply do not fall fast enough after peak pressure. Instead, they are well rounded near the peak pressure.
I found no suitable high pressure traces on the
RSI page. The 7 STW plot there is interesting but suspect. The shape of the pressure curve (excluding the spike) demonstrates QL's limitations. Using the two available Nosler bullet weights and looking at several powders, I cannot get a pressure trace from QL that has the
very slow fall off in pressure recorded nor the (astounding) indicated muzzle pressure. With the slowest ball powders, QL is predicting burning with the bullet well down the barrel.
