The physics of it are not at ALL hard to visualize, as you say, and applying reducto ad absurdum to either extreme (twisted VERY fast or VERY slow) illustrates this.
One thing to remember WRT the theory, is that friction robs velocity, while resistance (and hence, pressure) adds it. Is a faster twist increasing friction, or resistance? The bearing surface of the bullet against the rifling may increase a tiny bit, which increases friction and decreases velocity, but so does resistance to forward motion increase, which also increases pressure, which means more velocity. At the end of the day, the physics of the whole thing says that the two opposing forces pretty-well cancel each other out.
Not to mention that these factors are very minor in how they affect velocity, when compared to the larger factors at play like chamber, throat, and bore dimensions, etc. Twist might become a significant factor in velocity if you were comparing a 4" twist to a 14" twist, or something, but a 8" twist versus a 10" twist would be so inconsequential that it would be lost in the resolution of other factors.
I don't think it's that simple. Again, to take it to extremes, imagine a brrel with lands and grooves but NO twist. It's a straight "slide" on outta there for the bullet. Conversely, let's imagine a rifle with a 1:.1" twist (one turn every tenth of an inch). That bullet faces massive rotational angular deflection (compared to just going straight down the tube), as well as essentially rubbing against a lot MORE barrel- IE friction.
Your point to pressure seems valid EXCEPT that usually, with normal single-base powders, the pressure has a pretty early peak. By the time our poor 1:.1 twisted bullet is doing that last miserable 10" of barrel it's got minimal pressure behind it...
I would agree that it'd be unlikely to sort signal from noise comparing a 1:8 to a 1:9 or something silly. 1:7 compared to 1:12, maybe not.
It's all just MM. I'm not setting up a hill to die on here (sorry folks, grin). I know a couple people who've built a lot of rifles who say no difference. I know a guy personally and have for over a decade who is a complete loon, has built chitloads of rifles and run them hard, who does report seeing a difference. So, it's interesting to talk about but in the end, pretty meaningless in the big picture.
It's like listening to a virgin explain how to eat puzzy...
Travis
Eatin box and losing virginity is two different critters
