I learned about propelling charges for the 155mm howitzer this morning into the wee hours.
We've been using the same bags for decades. If it's not broke, I guess.
Howitzers are different from tank guns in that you can tailor the charge to the shot.
I haven't sussed out the details of it, but...
Howitzer ranges are broken into 'zones'. Conveniently enough they're numbered 1 to 8 from shortest to longest.
Ye Olde powder charges come in two bags. Green and White.
The green bag is the M3A1 and is, unequally, subdivided into five sections numbered from 1 to 5. Those numbers correspond to the zone.
The white bag is the M4A2. It, too, is unequally subdivided into five sections numbered from 3 to 7.
In the early '70's we added zone 8 to the mix and a red bag M119.
Rocket assisted projectiles created a need for a bag that would light the rocket so we added a zone 8S and the M203A1 (no relation to the under-barrel grenade launcher).
"Whooptydoo! But what does it all mean, Basil?"
Take your basic M107 high explosive shell, add a M577A1 fuse and shove it into your M185 cannon on your M109A4.
The lowest number on your propelling charge is the base charge and has a pad of black-powder which is readily lit by the primer you inserted separately after closing the breech. The lack of that BP pad on the other charges in the bag will keep you from using them later.
To fire in zone 1, you take apart most of an M3A1 charge and just use the section marked '1."
That will lob the 96.7 lb projectile 4km at a muzzle velocity of 211.8 m/s if you elevate the gun 673.6 mils.
Adding more sections increases the muzzle velocity and the range.
M3A1 Zone 1, 211.8 m/s, 4km, 673.6 mil.
M3A1, Zone 2, 237.7 m/s, 5km, 722.4 mil.
M3A1 Zone 3, 277.4 m/s, 6.5km, 690.4 mil.
M3A1 Zone 4, 318.5 m/s, 8.3km, 760.9 mil.
M3A1 Zone 5, 374.9 m/s, 9.8km, 717.2 mil.
M4A2 Zone 3, 292.6 m/s, 7.2km, 734.9 mil.
M4A2 Zone 4, 336.8 m/s, 8.9km, 736.8 mil.
M4A2 Zone 5, 393.2 m/s, 10.3 km, 756.1 mil.
M4A2 Zone 6, 475.5 m/s, 12.4km, 758.4 mil.
M4A2 Zone 7, 565.4 m/s, 14.8km, 760.3 mil.
M119 Zone 8, 684.3 m/s, 18.1km, 781.5 mil.
Or, translated to normal measurements... (rounded a bit)
M3A1 Zone 1, 695 fps, 2.5 miles, 37.89°. 4,374 yards for GURPS.
M3A1, Zone 2, 780 fps, 3.1 miles, 40.64°. 5,468 yards for GURPS.
M3A1 Zone 3, 910 fps, 4 miles, 38.8°. 7,108 yards for GURPS.
M3A1 Zone 4, 1,045 fps, 5.2 miles, 42.8°. 9,077 yards for GURPS.
M3A1 Zone 5, 1,230 fps, 6.1 miles, 40.3°. 10,717 yards for GURPS.
M4A2 Zone 3, 960 fps, 4.5 miles, 41.3°. 7,874 yards for GURPS.
M4A2 Zone 4, 1,105 fps, 5.5 miles, 41.4°. 9,733 yards for GURPS.
M4A2 Zone 5, 1,290 fps, 6.4 miles, 42.5°. 11,264 yards for GURPS.
M4A2 Zone 6, 1,560 fps, 7.7 miles, 42.7°. 13,561 yards for GURPS.
M4A2 Zone 7, 1,855 fps, 9.2 miles, 42.8°. 16,185 yards for GURPS.
M119 Zone 8, 2,245 fps, 11.2 miles, 44°. 19,794 yards for GURPS.
I think these are the max ranges. More powder at a lower angle might get less range, but a faster delivery.
For Twilight: 2000, what happens to the unused sections? I'm not even sure what happens to them today! Put them back in the can for recycling? The gunner has a table to use them up as needed?
Dunno.
But T2K will be using them and probably making separate BP pads to allow ignition.
The BP pad is 3 oz. of black-powder.
The breakdown of charges in the M3A1 are Charge 1, 1.3 lb.; 2, 0.4 lb.; 3, 0.7 lb.; 4, 1.3 lb.; and 5, 1.8 lb.
The M4A2 are Charge 3, 3.2 lb.; 4, 1.2 lb.; 5, 1.9 lb.; 6, 3.2 lb.; 7, 3.6 lb.
Since both bags use M1 powder, you could easily mix and match to get the correct charge for your shot.
This is more complicated than I'd wanted it to be, but I think I can make it clear in the conversion handout.
I also hope I can find this level of detail for the 122mm and 152mm Soviet ammunition.
I have far more detail than is needed for fuses. That's going to end up being representative of the three main types and skipping the 20-something variations of "mechanical time, super-quick" there are.
PS:
I have not included the M231 and M232 modular artillery charge system (MACS) bags here because they're too new for T2K.
1x M231 equals M3A1 zone 3.
2x M231 equals M4A2 zone 5.
3x M232 equals M4A2 zone 7.
4x M232 equals M119A2.
5x M232 equals M203A1.
Don't mix M231 with M232: BAD!