Originally Posted by
Tiger
Larry,
If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).
Take those times of flights (0.1875 and 0.125 seconds) and divide them into a minute (60 seconds) and then take the product of that division and multiply the 360 revolutions by it. You will see that the rpm numbers that appear are identical if you used the rpm formula which is in minutes.
I tried in a wrong way to say that the other day. No matter what velocity you shoot that bullet at to a 100 yard target, it still will only turn 360 times. The only thing that can change that is a difference in time to the target or a change in rifling twist of course.
Ralf