Optimist

Column of gas under pressure acts like a spring. Math says it's a spring. That's what didn't get discussed in the earlier examination of the problem. The nature of the springiness of the gas column (?) (my old English teacher would not like that construction, I 'spect....) in the short pistol length systems is much stiffer, at 20Kpsi gas in the column than the longer rifle length tube at 5Kpsi pressure at the tap. Short, stiff spring is going to give a mechanical system a totally different 'feel' than a longer, more limber one.

I've been shooting for a bit better than half a century now, and working on guns for almost that long. Since I got the cataracts repaired last year, I can see the sights again, so most of the lead goes where I want it to these days.... It's been a few years since I got involved in IPSC things, but it's time to go back to it.

The devil is in the details. You've pretty well covered the ground, but you left out a thing that is important for function of the gas system. The different gas tube lengths have different volumes, and they admit gas to those volumes at considerable pressure differential to achieve the same level of bolt manipulation. I'll put this in analogy form, though such is always suspect. If these were springs, the pistol gas tube would be a very short, very stiff spring. The carbine length is a bit longer, and not quite so stiff. The progression continues with the mid-length and rifle versions of the tube. The math gets very interesting when you start messing with gas flow and friction in these small vessels, but it is available in most of the physics books these days if you need to go deeper than this.