Using the momentum equations allows you to ignore all the other forces. It turns it into a blackbox system that can be analyzed. Considering that most of the other factors affect the internal ballistics of the gun itself (ie, a high engraving force can actually increase velocity because of the jump in pressure) that I'm not sure its a valuable exercise. As an engineer, if I were to spend the weeks necessary, im pretty sure my boss would be pissed. In a previous life I actually spent a few days drawing diagrams of the forces on a bunch of different parts. Trying to work all those forces together into a coherent mathematical system became a mess.
It was an interesting exercise, and I think the visiting VIP's were impressed with my whiteboard and the reams of math on my desk, but in the end, I'm not sure I learned much beyond the fact that most components of guns are radically overbuilt and that running an all-inclusive mathematical model of a recoil operated pistol would probably choke a supercomputer.
We can take an actual pistol, with a specific lot of ammunition, and take some measurements. We can get a pretty good pressure curve for the ammo, but if we do what Jim wants to do by boring out the rifling, that pressure curve is useless.
Add in the complexity from the fact that the range of ammunition a gun is expected to run well with is like expecting a V-8 to run on every flammable fluid from parafin to acetelyne, just by changing the muffler. ( there are something like 900 commercially available loadings for 9x19)
What do we know? we know that a 230 grain bullet at 800 to 850 fps, or any ammo with a similar muzzle momentum will run a stock 1911.
BTW, I think he's right. I'm pretty sure if you give the breach face a good whack, while never touching the barrel the gun will cycle just fine. All of the factors you are talking about go into calculating exactly what the necessary whack on an existing gun is, but its the hard way around to get there.
The force Tuner is talking about does exist. By worrying about the friction in the barrel you are approaching the dynamic system from the work and energy direction, instead of the momentum direction.
Using the momentum analysis is like using the stock market to measure the economy. All the factors are being accounted for, but its a black box. No one is sure what factor accounts for how much.
Trying to measure all the forces and frictions is like trying to measure the economy by interviewing every single person in the country. You know exactly how much each factor accounts for, but you spend so much time doing it that you never ever wanna try again. Economy? Screw that, i'm gonna watch the game!