Pic O’ the Day

SPC Gart Kamon from Bravo company 2nd Batallion 27th Infantry Regiment prepares to launch a 120mm mortar round towards insurgent positions at Outpost Monti in Kunar province on September 16, 2011. (AFP PHOTO/Tauseef MUSTAFA)

As you look at the round, you’ll notice 4 yellowish discs on the base of the round. These are propellant increments. By removing discs, you can vary the range of the round. There is a small charge built into the round itself. It vents through holes in the side of the round, into the mortar tube itself. That charge in turn ignites any propellant charges on the round. The fat part of the round forms a seal ahead of the burning propellant.

Rounds come with the maximum number of propellant charges already affixed, and they are removed as needed just before firing. After a shoot, excess propellant charges are burned- well away from the remaining ammo. The burn barrel is pretty cool to watch.

8 thoughts on “Pic O’ the Day”

  1. Thanks for explaining this one. Some day I’d love to be up close and present for this kind of thing. I learn so much more through tactile, visual, personal experience.

    1. Up close and personal is literally a blast when firing these 120mm mortars. You literally cringe inside when that round fires! The shock wave thumps down on your helmet. As soon as one round is out, the gunner levels the bubbles and the assistant gunner hangs the next round. It is physically tiring to do this in a big fire-for-effect as each round weighs about 32 pounds. Not sure since I am looking at this on a phone but it looks like all four increments of charge are on the round so this could be getting out to 7200 meters.

  2. I was told in OCS that the unused excess is burned, but never saw any burned. I had heard it could be neat to watch.

    The closest I came was some IMR powder I had spilled when I reloaded some 7×57 rounds in the carport of my parents house. I swept it up, then lit it and scared my little self to death when the small pile threw flames up from the concrete floor to the ceiling where they spread to about a 1′ diameter circle (about an 8′ ceiling no less). Fortunately, the flame lasted about 10 seconds and was over. I’ve been more careful about spilling powder since.

    1. It is fun to burn it but a bit rough. You pile all the charges up, crack one open and spread loose powder on it. Hit it with a match and …. whoomph!!! First time I did it, it burns so hot with a green flame that I wasn’t sure it was lit. I watched it until I was sure and then turned to walk away, thinkin I should run. No, I was too cool to run and the whole thing flared up like a solar flare behind me. It felt like it was searing my neck and I picked up my step a bit. But I did not run!

  3. Back when dinosaurs roamed the earth, I was a weapons platoon leader and the battalion 4.2 Inch mortar platoon leader. The weapons platoon had 81mm M29s (none of the fancy new kind of 81mm mortars) mounted in M125 tracks; the 4 deuce were in M106s. The 81s had 9 small charge bags of propellant and the 4 deuce had, if I remember properly, 64 charges, a base charge of six and then bunches of 2s sewn together for each additional charge with a bundles of 5 glued together. To adjust the range you would tear of a 1/4 of the sheet, 1/2 a sheet, etc. 1 quarter torn was 7/8s a charge; 3 sheets torn was a 5/8s charge So you would get a call for 81s that called deflection, elevation and “Charge 5!” For the 4.2 you could get deflection, elevation, cant and “Charge 32 and 3/8s!” If you used less than a a sheet you just toss in enough of those corners to make up the difference. There was a clip on the bottom of the charge extension off the shell whcih kept the charges on the round.

    That is why on of the prereqs to get into IMPC was to take a math exam that had you do a lot of computation of fractions. And it was all cold stick…no computers.

    We would burn off all the old charges. But we would line the charges in a line and set canteen cups of water near along with a large pot of water.

    After ignition, hot coffee and shaving water!

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