antelope sniper - I do understand the pressure curves but should've qualified my answer. I meant standard length barrels up to say 26 inch or possibly even up to 28 or 29 inches. I haven't attempted the maths but it doesn't sound right that friction would become the dominent force toward the end of the barrel when using a fast powder, to the point where it starts to slow the bullet down. It would eventually happen but I suspect the barrel would be unpractically long.
I say this because I have a couple of example firearms:
A 29inch barrel Mauser 8mm that always exceeds the velocity of standard barrels eg 150gn @ 3000fps.
I also have a 16.5 inch 9mm carbine that exceeds pistol velocities (not always by much though) and it uses a relatively miniscule amount of relatively fast powder, and has a large void behind the projectile to fill the gas with as it travels down the barrel.
Actually there's a website with published data for velocity versus reducing barrel length - some guys progressively chopped barrels and took readings, for several cartridges. I don't think they used any barrels longer than 22 inches, and sometimes there was minimal speed decrease at length decreases but I don't think the speed ever increased, if you know what I mean. I'll have to go back to their website though to check.
Go back and re-read the original string to which I responded.
The question was not about absolute velocities across barrel lengths, best velocity across power burn rates and barrel lengths.
