Bullet flight time conventions

[Rupert]

Originally Posted by Ulzgoroth

Also, 1/2d I'm given to understand is Not Done Right in a significant number of canonical sources and I'm not sure whether that's all of them or only a subset.

It depends on what you mean by 'not done right'.

If 1/2D range is looked at as being when the projectile has slowed to the point where it does half the damage it does at the muzzle, then many of the ranges will be wrong. 1/2 damage implies 1/4 velocity, which can be a surprisingly long way.

Also, strictly speaking the 1/2 range won't change when firing a given round in different weapons - initial velocity does not determine how far the bullet needs to travel before dropping to 25% of muzzle velocity, merely how fast and thus how much damage it did to start with. All bullets with the same degree of streamlining and same sectional density will have the same 1/2D range. Also, this mean that each halving of damage occurs after the same distance, so 1/4D range is double 1/2 range, 1/8D is three times, and so on.

BTW changes in atmospheric density will change 1/2D range, so at extreme altitudes and on other worlds it will be more (low pressure) or less (high pressure).

Max range changes with air pressure and with gravity, and unlike 1/2 range does depend on muzzle velocity (as well as streamlining and cross sectional density). Thus 1/2D range shouldn't change between weapons firing the same round, even when they have radically different barrel lengths (e.g. firing a pistol round from a carbine), but max range should.

I think that in practice 1/2 ranges have tended to reflect 'effective range' from literature, and a bit of the 'intuitive' 'longer barrels make things go further' and 'big bullets go further'. For example, in HT (which is otherwise pretty good), the G3 has a shorter 1/2D range than other 7.62x51mm battle rifles, and the Model 70 Winchester firing .458 Winchester is given a very long 1/2D range as is the .600 Nitro Express, even though they both fire quite poorly streamlined bullets - that's why long range large game shooting tended to use .375 H&H and similar rounds.

Re-doing all of this to make everything dead-consistent is pretty much pointless, and a huge amount of work for little gain.

Max range is a maximum range at which you can use the weapon. It usually factors in both projectile ballistics and what elevation is usable. I have no information about what book authors actually do with it in many cases, but that's what it tells us. It absolutely isn't maximum range for a shot 'parallel to the ground', that's not how projectile weapons are used in any context where maximum range is a consideration.

Attempt to find a maximum range in a good source is what they do, I think. Failing that, make an educated guess based on what similar weapons manage.

For UT weapons any 1/2D is going to be an approximation, and max range an approximation off that approximation. There's no sensible way around this.