Bullet flight time conventions

[Joseph Paul]

A couple of current threads about TL8-9 weapons and others made me curious.

What are the current conventions and assumptions about bullet flight time in GURPS? What do you use?

Just what does Max Range represent in GURPS? The furthest reach of a normal firing of a round parallel to the ground? Or the deliberate attempt to get the most range out of it by firing in an arc?

RAW for firearms is that Max range can be reached in one turn of one second's duration. Frankly, while playable, it implies some very implausible muzzle velocities. And that gets worse with ETC and ETK options. What were Mr. Pulver's ideas on where muzzle velocity would go in the future with UT (and range and damage) and why?

Flight time issue - with the advent of Guided and Homing munitions in UT flight time became an issue. No longer limited to just specific missile weapons in Basic any firearm can add these options to it's ammo.

On the one hand that still creates some highly improbable muzzle velocities. The 15mm AM rifle has a 1/2D range of 2000 yards that would be a 6000 FPS muzzle velocity. Modern cartridges are topping out at 4000 FPS and they have severe limits on their actual range - some of those have a poor ballistic coefficient that limits the range to a few hundred yards.

On the other it is not possible to explain why a round that could do 9000 yards in a second now takes 4.5 seconds to cover that distance just because there is a homing package on it that adds no weight and doesn't change the damage. So that is some cognitive dissonance.

Tactical Shooting (a book I don't have so I may be mistaken about the details) introduces a bullet flight time standard of 250 yards per turn for handguns and 600 yards per turn for rifles to use in figuring bullet flight time. 1/2D Range has no effect on rounds that are not Guided or Homing, use the 250/600 divisor to find how many turns it takes your round to arrive. Does TS give any changes for missiles etc that would use 1/2D Range as the divisor to find flight time?

Guided and Homing - for missiles with switchblade fins and active controls it is pretty easy to see that they have some good capability to make some pretty hardy deviations to follow a target. However a number of firearms opting to use G&H ammo are not set up for that kind of control surface. At best they will have some small active system producing thrust for maneuver through the time of the flight that can be used or with TL9+ materials active surfaces that induce drag to make changes. Either way the degree to which the round can change direction is limited and the high velocity of some 1/2D Ranges should shrink that capability further. Should we be thinking in terms of a circle of possible correction that shrinks each turn until the round hits or runs out of range? That would also give the target opportunity to break the contact - the sensor may still detect the target but it can't produce enough correction to actually hit.

I see the possibility of defining muzzle velocities for some of these weapons and playing with variations. I am wondering if there is a muzzle velocity advantage that I can give to EM firearms that will keep them ahead of conventional firearms and even with ETC/ETK?

Or is it more reasonable to limit the advantages of ETC/ETK to one or more of damage, increased 1/2D range and not much extension of Max range citing problems with ballistic coefficients at those speeds/mass/length of bullet? Or reducing the multipliers for ETC/ETK?