Pressure does NOT equal velocity. Some powders produce higher pressure to achieve the same velocity as others.
There are a lot of things that can affect pressure.
Temperature, altitude, chambers, bores, and i'm sure there are others also.
Example of temp: Friend of mine had a near book max load he developed for a rifle in early spring, no pressure signs. In July he went out with same load to do some penetration testing, primers blew out and it was all he could do to open the bolt.
And yes there are slow and fast barrels.
2 of the Reminton 700 30-06's in my house shoot the same load of IMR 4350 in R-P cases, with the same primer, with a 165 gr Hornady. One of them gets 2720 fps the other right at 2900 fps, and they both have 22" barrels. The load shoots accurately out of both rifles.
Pressure = Velocity
There's no way around it. No one is talking about comparing different powders - this is about book powder charges not reaching book velocity. Loads that shoot fast in high heat do so because of high pressure (caused by the xs heat).
There's no such thing as a "fast barrel" or a "slow barrel". There are barrels with tight cut chambers and precison bores that make max velocity (and pressure) w/ a minimal powder charge and there are sloppy cut chambers and sloppy bores that make less pressure and less velocity with the same powder charge. The powder charge to reach the same velocity can vary significantly, the pressure will be close to the same.
David
