How does a Mortar Tube work?


April 23, 2003, 08:05 PM
I've been puzzling about this. Any Eleven Charlies here? (I believe that's the correct Army MOS for Mortar Infantry.) I mean, you have the tube, you drop the shell in, and the whole shell fires out of the tube, and goes quite a distance sometimes. What, exactly propells it? I'm assuming there's some kind of propellant in the shell. Does the shell have like a soft rear end that works as like a tail pipe when it's fired?


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April 23, 2003, 08:11 PM
The fixed firin pin is located in center of bottom of the tube, mortal shell has primer/propellant located in base of shell. Gravity causes shell to fall to bottom of tube, primer strikes fixed firing pin.....boom!

April 23, 2003, 08:12 PM
Okay, simple enough. Was just curious? Have never seen one up close?

Mike Irwin
April 23, 2003, 08:25 PM
There are actually a number of different types of mortars...

The ones most commonly in service now are fin stabilized, drop fired.

Propellant and priming cap is contained in the rear stem of the shell.

Some mortars can be fired either by a lanyard with a trip firing mechanism or have the firing pin locked up in place for drop firing.

I believe the German WW II era 50mm Granatwerfer had a trigger firing mechanism as the tube was too short to ensure a drop fire.

Other small support mortars have also used a mechanical firing device over drop firing for the same reason.

Finally, not all mortars are smooth bore fin stabilized. Some very successful mortars, such as the American 4.2" of WW II, were rifled and used an expanding driving band to engage the rifling on firing.

April 23, 2003, 09:00 PM
Mortar bombs have propellant bags attached to the base. They are pulled off in increments to adjust for the desired range and trajectory.

Navy joe
April 23, 2003, 09:15 PM
No offense to you Night- I just find it appalling that infantry is not cross-trained in the basics of other front line combat arms. Sad, but typical military.

50 Shooter
April 23, 2003, 09:20 PM
Here's one for you to guess.

April 23, 2003, 09:24 PM
Okay, so what do you do when you have a misfire? Do you upend your mortar tube to get it out?

Greg L
April 23, 2003, 09:28 PM

That's cool. What kind of range can you get from it? Is that the gas line coming in on the left (white pipe)? Kind of puts the run of the mill spud gun to shame.


April 23, 2003, 09:30 PM
Night- I just find it appalling that infantry

No offense taken. I'm not infantry. I'm a combat engineer. We do some infantry stuff, but we're not trained on the full battery of infantry weapons. On the same token, infantry doesn't get all the demolitions and mine warefare training.

Jeff White
April 23, 2003, 09:34 PM
The Army currently uses 3 different mortar systems. At company level in light Infantry units you have the M224 60mm mortar. It can be fired by dropping the round down the tube, or you can set it up to be trigger fired. It comes with two baseplates and a bipod. In the assault mode you don't use the bipod and you sue the small baseplate. You aim it by holding the tube in your hand and lining it up visually...this is when you use the trigger fire mode.

From the bipod, you use the mortar sight and aiming posts. This is much more accurate. Charge, deflection and elevation are computed by the Mortar Ballsitic Computer or manually through the use of maps and Graphic Firing Tables.

The M252 81mm mortar is found at Battalion in a light Infantry unit. This is a British design. It can only be fired the conventional way, by dropping the round down the tube.

There is also a 120mm mortar used in heavy units. This is an Israeli designed system and comes in a towed version or mounted in an M106 mortar carrier (M113 variant).

The mortar round is shaped like a little bomb. The bottom of it is hollow. There is a primer at the bottom. The increments (charges) are little bags of powder tied to the sides of the holow part by string. The FDC computes the charge and the mortar crew removes the increments so the charge is correct. The gunner sets the correct deflection and elevation on the sight, levels the bubbles and the assistant gunner drops the round down the tube. The primer hits the firing pin, the flame goes up the hollow base, igniting the increments and the pressure builds up behind the round and it leaves the tube.

As was mentioned before the round is stabilized by fins in flight. The tubes are smooth bore.

At one point we used the 107mm or 4.2 inch mortar at Bn level. It had a rifled tube and the rounds had no fins.



The mortar

50 Shooter
April 23, 2003, 09:45 PM
If you look near the base of the tube you can see canon fuse sticking out, it has been upgraded to a flapper type firing device using a canon primer to fire it. While it's not mine (I need one though) the guy that owns it just recently finished it, the pressure test was 1lb of black powder and two bowling balls. He said the balls flew about 1200 yards!!! The one that another person owns will shoot a ball about 700 yards on a 1/4lb of black powder.

We'll be out shooting them soon, I'll try to catch one as it fires and post a pic.

April 23, 2003, 10:22 PM
Misfires? I recall that having the least senior member of the crew kick the tube (to dislodge a hung round)was one of the options. If that doesn't work, then, after waiting to see if nature will take over & the dang thing will shoot, the base plate would be unhitched, the tube tilted so the round would (hopefully) slide into the waiting thumbs of a very nervous gunner.

One time I saw the crew of a mounted 4.2 deal with a hang fire by closing the doors over the tube & driving away.:what:

The amazing part is that they didn't get blown into ragged little bits......

April 23, 2003, 11:10 PM
Never got near one of these as an enlisted guy, when I went through ROTC advanced camp we got one day of training on these, and at one point I actually ended up being the guy who had to drop the round down the tube - when you see what one round from an 81mm can do, it makes you VERY respectful and careful with the ammo! They are also LOUD, and I don't mean 'loud', I mean LOUD! I guess it's the muzzleblast but man even with earplugs and shoving my fingers in on top of the earplugs after a few rounds my ears were ringing for the rest of the day - I do NOT know how 11C's handle this stuff without going deaf!

April 24, 2003, 01:27 AM
hey 50 shooter

does your buddy have that design on paper at all. I have a machinist pall that needs another project.


April 24, 2003, 02:05 AM
The increments (charges) are little bags of powder tied to the sides of the holow part by string. The FDC computes the charge and the mortar crew removes the increments so the charge is correct.

I was able to play with mortars just a few times while I was a reservist with an SBU as we had a 60mm tube on a mount back aft on the MK III PBs. I remember instead of "bags of powder" small packets of what seemed to be plastique(??) the size of a stick of Trident gum for propellant.

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