The lift charge used to lift a mortar shell is incremented so as to provide
a more precise control of the aiming of the shell.
Think of it this way...A maximum lift charge with the appropriate angle
might land a shell miles into the distance. Now, what happens should you
want to land one just a few hundred yards away?
You could just elevate the mortar higher...maybe even to 89 degrees (almost
vertical) but then, with the maximum lift charge, your shell is going way,
way up into the air and is influenced by wind, heat rise, etc, etc.
Crap...it might even land on you! Aiming to fractions of a degree so as to
hopefully land within dozens of yards of your enemy would be practically
impossible. This is a terribly inacurate and unreliable way to lob a mortar
shell. In fact, it's not done.
Instead, you keep the gun to a typical firing angle and simply reduce the
"lift" charge. Instead of flying miles, the shell now flies only hundreds of
yards.
To hit a target reliably, there needs to be a combination of angle and lift.
One is not more valuable than the other. However, the proper combination
will provide accurate fire. This is where "the tables" (or "experience")
come in to play.
The increments for these rounds contain smokeless powder. It's like pulling
the bullet off a pistol cartridge and pouring the powder into a plastic
baggie. Not the most ideal thing to carry in your pocket, but it isn't going
to do ANYTHING but burn fiercly in your pocket should it be ignited.
DETONATION is a process where the energy of an explosion exceeds the speed
of sound. It is damaging in all cases and is useless to us unless we want to
destroy things.
DEFLAGRATION is a process where energy is released from a source at less
than the speed of sound. It is "ooph", "thud", "bang" and "lift".
A firing gun uses deflagrating propellants to launch a projectile. It's true
that smokeless powder has more energy than Black Powder. However, it is
absolutely wrong to think smokeless powder detonates...because in that case
you would be standing next to a 60mm pipe bomb. Place a stick of dynamite in
a 2" steel pipe and stand next to it while it goes off. Notice a difference?
BTW, smokeless powder as well as mortar increments are all perfectly legal
to own. They are not explosives, they are propellants.
The propellants used for mortars are fast burning, like pistol powders. They
burn fast, but in a large tube (compared to a pistol barrel) only manage to
fill it with enough pressure to "lob" a shell out. It's similar to the HI-LO
effect in a 40mm grenade cartridge. This is not pistol, rifle, or artillery
gun pressure. Those kinds of pressures would blow the little thin-walled
mortar apart.