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in Vietnam, the max charge was always the goto charge. never exactly knew why, and I spent an agonizing six weeks in the FDC section. On a typical towed 155 unit you shot four white bag charges for every single green bag charge. I've shot white at 3000 yards and out to 14,000 yards. Yet I've shot green bag from 100 feet to 3000 yards.

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As a former Fire Direction Officer (FDO) who ran an FDC in Germany for a year I can answer that question. There are two reasons you want to use the HIGHEST charge possible when calculating firing data.

For any given range to the target there are usually two or more possible charges (or number of powder bag increments) which will reach the target so you CAN select any of them.

However the more increments you use, the higher the muzzle velocity of the round when you fire it and while it would seem that the answer is that it gets the round there FASTER, and that's true, the difference is not more than a few seconds.

The primary reason for using a higher charge is that because of the faster muzzle velocity, the round will not drop as far during the (shorter) time it takes to get there, meaning instead of having to point the muzzle higher in the air, you can shoot with a flatter trajectory. The faster and lower trajectory makes it MARGINALLY more difficult for a counter fire radar to detect your position, although I'm certain that the technology of today makes even that less of an issue.

A flatter trajectory is also better if you have to use a MECHANICAL time fuze and you're looking to get a 50 meter height of burst. If the round is coming at the target in more of a "down" angle as opposed to an "across" angle, a very small difference in the time setting can make a big difference in the height of burst. Variable or Proximity fuzes don't have that problem.

And the OTHER reason for using a higher charge is simply fewer left over bags which are hanging around in the pit and have to be laid out and burned.

175 mm Propelling charge canisters (most are packed in wooden wrap) :



and here you can see the Propelling charge "white bag" (at least I think that's what is is ) laying on the M107 folding crew seat :



H.P.

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.
As a former Fire Direction Officer (FDO) who ran an FDC in Germany for a year I can answer that question. There are two reasons you want to use the HIGHEST charge possible when calculating firing data . . .

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Was there any consideration for the faster barrel wear (from using higher charges) when choosing the firing data?

KL

great post Sir! I never knew why, and the only thing I ever could come up with was an easier bore calculation for tube life. We usually went for a 20 meter height of burst, but have heard that burst rate was all over the place. I've even seen three howitzers shoot a time fuse while the other three shot PD on a rare occasion.
gary

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great post Sir! I never knew why, and the only thing I ever could come up with was an easier bore calculation for tube life. We usually went for a 20 meter height of burst, but have heard that burst rate was all over the place. I've even seen three howitzers shoot a time fuse while the other three shot PD on a rare occasion.
gary

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Brain fart! You're right of course, it should have been a 20 meter HOB, good catch.

While as mentioned, we did keep track of rounds and charges fired and checked for wear to make sure that we didn't lose too much muzzle velocity, I don't recall ever really being directed to stay away from higher charges for that reason. But depending on where and when you were, that certainly could have been part of the decision.

ever shoot those plastic tipped fuses that sent out the radio beam? I remember plotting them in FDC, and of course I've shot them.

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ever shoot those plastic tipped fuses that sent out the radio beam? I remember plotting them in FDC, and of course I've shot them.

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Yeah, those are VT (Variable Time) or "proximity" fuzes. As you said they send out a signal which when a strong enough return is received due to the designed proximity of the fuze to an object, causes the fuze to set of the round. You can set an actual time value and it will go off at that point even if it's not that close to the ground, but of course the object is to get a precise HOB above the ground so you can get the proper effect on the target, usually troops in the open with little or no overhead cover.

In the 70's we still had a LOT of the old Mechanical Time fuzes and as they were cheaper, we mostly use them, but we always had some VT fuzes around.

Those things were developed in WWII, primarily for anti-aircraft usage. Trying to get shells to detonate at the same height as an airplane was pretty damn hard in the early 40's as first you'd have to "guess" how high the planes were, and then try to get the shells to go off at that altitude.

The ability to miniaturize a radio transmitter and receiver which would fit into a fuze AND withstand the forces on firing the projectile was a significant accomplishment. It was such a secret that initially the US only allowed the NAVY to use them with the idea that if the shell somehow never went off, there would be no chance of the enemy recovering the fuze intact as it would go into the ocean. Eventually it was finally authorized for ground units in Europe to great effect.

So---you sit back and relax with a live round with an armed radio proximity fuse in the tube?

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So---you sit back and relax with a live round with an armed radio proximity fuse in the tube?

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They are bore-safe, meaning they can't initiate until fired, plus the VT fuze isn't "armed".

For mechanical fuzes (US spelling) they need to see some combination of g-force and rotation to get the various internal parts to line up such that the primer can fire. VT fuzes use batteries that need g-forces and rotation to release the electrolyte and mix it with the electrodes. Otherwise, there's no power in the fuze.

The main problem with ramming out a VT fuze is the fragility of the fuze and, if I recall, the shape, which is not a good fit with the ramming cup.

KL

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So---you sit back and relax with a live round with an armed radio proximity fuse in the tube?

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They are bore-safe, meaning they can't initiate until fired, plus the VT fuze isn't "armed".

For mechanical fuzes (US spelling) they need to see some combination of g-force and rotation to get the various internal parts to line up such that the primer can fire. VT fuzes use batteries that need g-forces and rotation to release the electrolyte and mix it with the electrodes. Otherwise, there's no power in the fuze.

The main problem with ramming out a VT fuze is the fragility of the fuze and, if I recall, the shape, which is not a good fit with the ramming cup.

KL

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So---you sit back and relax with a live round with an armed radio proximity fuse in the tube?

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They are bore-safe, meaning they can't initiate until fired, plus the VT fuze isn't "armed".

For mechanical fuzes (US spelling) they need to see some combination of g-force and rotation to get the various internal parts to line up such that the primer can fire. VT fuzes use batteries that need g-forces and rotation to release the electrolyte and mix it with the electrodes. Otherwise, there's no power in the fuze.

The main problem with ramming out a VT fuze is the fragility of the fuze and, if I recall, the shape, which is not a good fit with the ramming cup.

KL

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So like a 40mm grenade it's got to be fired and start spinning to arm it. Tho unloading a grenade launcher is probably a bit easier than a cannon.

As for a fuse being safe unless it's fired; I can vouch that a fused up round will explode from heat alone.

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As for a fuse being safe unless it's fired; I can vouch that a fused up round will explode from heat alone.

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That's not a case of the fuze "functioning" though. There is a complete explosive train in there, down to the sensitive primary explosive in the initiator. If it gets hot enough it will explode. Much like a propane cylinder is safe - unless you put it in a large fire.

Some modern fuzes are designed so that it is not just the mechanism that is held out of line until fired, the primer/initiator is as well. So, even if the most sensitive part of the explosive train explodes because of a unplanned event, the train will not progress.

KL

Man glad I asked keep it up.

If not so old got me wanting to join the Artillery.


Jeff

Can't add to that

Except thanks for your service.

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Can't add to that

Except thanks for your service.

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Been asked to write a book several times, but I still refuse to. Yet if I did, it would be nothing but funny stuff. No one needs or wants to know about my nightmares. But if you wanta talk about loading a barrel up with dead rats and shooting them due west; then I'm in.

I will tell you up front that the only reason I'm writing right now is from my second First Sargent. He busted my butt 24/7. He taught me the right way to do everything, and made sure I did everything his way. Glad it only lasted 15 months.

gary

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Can't add to that

Except thanks for your service.

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Been asked to write a book several times, but I still refuse to. Yet if I did, it would be nothing but funny stuff. No one needs or wants to know about my nightmares. But if you wanta talk about loading a barrel up with dead rats and shooting them due west; then I'm in.

I will tell you up front that the only reason I'm writing right now is from my second First Sargent. He busted my butt 24/7. He taught me the right way to do everything, and made sure I did everything his way. Glad it only lasted 15 months.

gary

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Gary, thanks for your service.

I'll buy you a six pack of Tiger beer with a glass of ice for that rat story...

I love this!!!!

I also HATE monkeys. I was a merchant seaman and went down to the PI shortly after the base closure. we ported in Olongapo and worked with an ex-pat doing some of the SCUBA jobs. We were bunking with some Marines who were still on cleanup in the area, policing the base as it got parted out.

Every night there were these monkeys that would raid the latrine and garbage pit. Not the cute zoo-monkeys, but the big bite-your-face-off ones. If anyone hated them more than me, it was the Marines.

So, we brought in a batch of beer n' whiskey and shared with our mates, and on the 3rd night there, the monkeys were out in force. We were out at the fire pit and you could hear them on the ground, in the trees, and on the roofs. The Marine Sergeant had enough and took an M68 hand grenade, pulled the pin and stuffed it in a used MRE pouch (it was Beef Diced, with Gravy). He marched off into the darkness and came back a while later. We were all silent as we waited. Soon...came a faint 'pop' followed by a concussive THUD!

The jungle went quiet for a moment and the monkeys were all silent for the remainder of the night. We shipped out the next day, and on the way there was an Army intel guy on the docks. He asked "How was your escort?" I replied "Hot chow was a f*ckin' blast."

I owe you a sixer my friend.