Quote: Source data I have other than from Roger Stowers just references the barrel length.
In Roger's work he makes this comments: "To measure velocity for his cartridges Gibbs would load to 53,500 CUP (~63,800 psi) on his own equipemnt, then go to Speer and use their Potter chronograph. His avertised velocities are questioned to this day. Many believe the velocities Gibbs advertised are unattainable. Many of his velocities were corrected from instrumental to true muzzle velocity. This added a few FPS. He considered barrel length as the distance the bullet traveled down the bore, not the distance from the bolt face to the muzzle. That in effect added two more inches of barrel length and another 100 fps or so. Instead of taking the average velocity of 10 shots Gibbs recorded the highest speed achieved."
I have nothing where Gibbs stated these facts but, assume that Roger did his homework. Using my wildcat with basically the same capacity I can dupe Rogers velocities and by adding 2" I can calculate speeds published directly from Gibbs.
I either missed this statement, or have forgotten it! (Probably the latter!!)