Scott, Yes, we might max out before the full 48" of the barrel is used. If the velocity is trending the same as the .22 did ( 1745fps, 7.5gn, .22, 23.3", 26cc, 4500psi, 70% system eff) then the identical trend in the .278 barrel ( 6.5gn, .278, 47.4", 48cc, 4500psi, 70% system eff) should be about 2166 fps. I also doubt it will be that fast, because I think the system efficiency will start dropping quickly in relation to the velocity. My fudge factor, or your fudge factor? They are pretty close, so it might be a coin toss. Scott, try running your numbers with a .278 bore and see what you get.Charles, yes, kinda off topic. Shows me the 45 acp is behaving like a pistol cartridge should. Lloyd
.... As long as the pressure at the base of the bullet exceeds the drag of the bullet in the bore, it should keep accelerating, the way I see it.... The only question is at what point does the fluid friction (including any possible sonic effects) in the barrel reduce the net force on the bullet to zero?.... Bob
you can not break the speed at which a molecule can travel and at any given pressure that is the speed of sound
Let me propose a thought experiment, to do with the average RMS molecular velocity of air.... Take a basketball full of air at 70*F.... The average molecular SPEED is 1650 fps, in random directions, bouncing off each other and the inside of the basketball, causing the pressure to hold it stretched tight.... The average VELOCITY of all the molecules, put together, must be ZERO, however, or the basketball would be moving / rolling / oscillating.... I am using velocity here as a VECTOR, and the vector sum is zero at any given instant.... Now take the ball to the top of the Empire State building and toss it off.... Let's assume it reaches a terminal velocity of 150 fps.... The molecules, relative to the ball, still have an average SPEED of 1650 fps, and an average VELOCITY of zero.... but relative to the ground, they have an average VELOCITY of 150 fps.... That means that the average velocity of the molecules, relative to the ground, is 1800 fps....Now drop that basketball down a pipe.... in a vacuum.... accelerated by gravity (or the vacuum, or external pressure) to a velocity, relative to the pipe of 2000 fps.... If the velocity of the molecules cannot exceed 1650 fps absolute, relative to the pipe, then once the ball reaches that velocity, there should be a net force slowing the ball, applied by the air molecules inside the ball.... I submit, just using simple logic, that is not the case....Now line up many basketballs in the pipe.... same thing, right?.... You now have a whole bunch of air molecules, travelling at 2000 fps relative to the pipe.... Now take away the shell of the balls.... Is it reasonable to assume that suddenly there is a limit to the flow of 1650 fps, imposed by the random motion of the molecules?.... I would suggest that is not the case, because the SPEED of the molecules, relative to their center of mass may be 1650 fps.... but the mass itself is moving, so the pressure those molecules can exert in the forward direction is greater than what they exert in the backwards direction.... That force can come from gravity, a vacuum, or pressure.... and in the case of our barrels, it comes from a pressure differential between the reservoir and the air in front of the bullet.... The force accelerates the bullet, AND THE MASS OF THE GAS, while not breaking the 1650 fps "speed limit" of individual molecules, because that speed MUST be measured relative to the center of mass of the expanding gas column.... As I said, I think you can explain all this with Newtonian Physics.... and I submit that the above is very likely why the "old idea" of a speed limit to air in a pipe is 1650 fps has been so easily broken.... In fact, if the air is expanding (as in driving a bullet), I would suggest that the limiting speed of the bullet may be TWICE the 1650 fps random SPEED of the molecules.... because the center of mass of the expanding air can reach 1650 fps, with the average molecule expanding away from that center of mass at 1650 fps.... The ones at the closed end have zero velocity.... and the ones behind the bullet reach 3300 fps.... Now I realize that friction losses would prevent us from ever reaching that.... but isn't the concept valid?.... and this for EXPANDING air....Taking it further, then, if you are continually adding air (pressure, ie a force acting on the molecules at the breech end), giving them additional VELOCITY toward the muzzle (ie adding a vectored energy).... you should be able to approach the above state even easier.... because you are doing it continuously.... At some point, yes the FLOW velocity will reach the speed of sound, but even then, the molecules against the bullet will be flying away from the center of mass (which is travelling very quickly) at 1650 fps (or nearly).... I may not have described the sequence of events perfectly.... but I think RELATIVE motion of the molecules to the center of mass of the air is the key.... After all, Relativity is only a limit when you approach "C", not Mach 1....Bob
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