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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!
Since you (sort of) asked:
ReplyDeleteYou've got the fundamentals down perfectly, and the firing tables anticipate low angle and high angle fire, consulting which tables is how the FDC (Fire Direction Center) does their magic, and issues the fire command, which incudes the powder charge by color and increment number (probably exactly like mortarmen do).
The extra bags for each shot are held up by the powder monkey (i.e. the bootest flunkie on the gun crew) well to the rear of the piece, and dropped in a purpose-dug powder pit afterwards, once the Plt. Cmdr. has sighted them, visually verifying that the gun crew is not going to send a short round into the FOs (and troops, in combat), nor send out a hot round in peacetime, and drop an HE shell on the PX, or the nearby community.
When firing is complete at that position, or for the day for multi-day positions (only in training), the bags from all guns are collected and are lined up end to end, one of the bags (of rabbit-chow sized gunpowder pellets) is cut open, and the whole daisy chain lit off in a spectacular burn that rivals WP welding in brightness intensity.
The BP booster is because the primer (a .410-sized brass charge) will only light that increment, and if it's placed too far up the tube, put in backwards, (or left to one side rather than loaded by one of your motivated idiots - ask me how I know this) by the powder monkey, you get a misfire.
That's why the penultimate call before the "Standby" and "Fire!", is to be "Charge X _____ Bag, I see Red!", meaning the powder monkey has correctly inserted the propellant charge into the breech before the #1 man closes the breech and primes the beast to fire.
Oh, and the reason they're not used nor reused, is that being hygroscopic, the ordinary moisture absorbed by the powder charge would render their future power factor rather unpredictable once they've been out of the can awhile (except maybe in a very arid desert), in a "you're going to get a short round" kind of way, which is why they're just burned up, and why you generally don't cut charges earlier than the actual fire command, but rather leave them sealed in their tube as late as possible, unless a "Sweep and Zone" is coming down, meaning you're going to rapidly fire off generally something between 9 and 25 rounds in a grid pattern, in a foreshortened time compared to normal operations, to erase an area target. Gun bunnies love those; the recipients, not so much.
ReplyDeleteIn the post-apocalypse Twilight: 2000, saving that stuff is going to happen. Even if it's a bad idea.
DeleteNow I wonder how long it takes to suck up water from the air.
If nothing else, it might make a dandy fire-starter and there's bound to be lots of it around since there's been a war on for a couple years all over Eastern Europe.
I may have seen a few pellets of "accidentally" spilled powder used to jumpstart a wood fire or two in the field back in the woods in a firepit, esp. if the wood was wet to start with.
DeleteA bag or two was usually similarly used when we had a crapton of wood dunnage (shell and pwder tube pallets, spacers, and such) to get rid of in a burn pit after a lot of firing.
And anytime we were in the field between November and March, particularly one memorable day when I was assigned to clean out all the puddles in the position, which I did by taking my e-tool and flipping all the now-frozen puddle discs out of the mud and carrying them over to low ground (because after it rained the temps dropped into the teens), the daily and nightly powder burns were attended closely by most of the platoon or battery in question, because a three-bag wide 100' long daisy-chain of the increments of that powder burns hot, and that was the warmest some of us got all day.
In a Twilight scenario I'm sure that stuff would get re-cycled, but accuracy - never a strong suit of artillery anyways, until laser and GPS guidance of late - would go all to shit.
Oh, and FWIW, there's also a supp(lemental) charge in the pointy end of the Comp B in the HE shells themselves, which had to be removed (and also got burned with the excess powder increments) in order to insert and seat a standard VT fuze, which was a couple inches longer than the PD or MTSQ fuzes. Those little things were about 2" across, and about 3" deep (shaped like a ½ can of Red Bull), with a little plastic pull-out finger strap across the top. They were sealed in plastic, and I suspect in a pinch they'd make handy ½-pound demo blocks for homebrew satchel charges and such.
The unused charges, like unused mortar charges, get burned at the end of firing. If overly inventive privates or local malcontents get their hands on a mass of defacto incendiaries nothing good is going to happen.
ReplyDeleteAfter WWII and during his college years, my dad served in a Louisiana Nat Guard 8"howitzer unit. One day they figured out the best powder charge to get the round to the target and handed the powder and angle solution to their trainer. Said trainer kindly (most likely not, actually) pointed out that there was a large hill between gun and target so the powder charge was too high for lofting and the round would impact on the front of the hill. Howitzer gotta shoot up and over
ReplyDeleteHe also got to meet one of the women calculators that worked on the powder/elevation charts for said howitzer.