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British 3 inch Ordnance Mortar' firing pin

D

Draoich

Member
Hallo,
I previously posted the following in another forum here:

I understand that the Ordnance 3 Inch ML Mortar of WW2 was adapted in 1944 so that it could then fire captured Italian 81mm mortar bombs. The internal diameter of the barrel was already the same (or near enough) to allow the bombs to fall down onto the firing pin but the arrangement of the firing pin in the British tube did not suit the percussion cap in the primary charge of the Brandt' type 81mm bomb. Does anyone have any further information as to why the Brandt' type bomb would not fire on contact with the original firing pin of the 3 Inch mortar?

I now have found the answer:

In the later part of World War II the British modified the 3-inch mortar to allow the Mk. V to fire captured Italian and German 81mm mortar ammunition (the modification required a change to the firing pin design as the anvil was part of the ignition cartridge in the original British design). Prior to this, the base cup of the British 3 inch mortar was fitted with a firing stud which did not contain a firing pin to act on the percussion cap in the bomb (unlike all other 81mm mortars). This firing stud was about 3 inches long and had a flat end which acted as a percussion plate instead. The percussion mechanism was fitted to the primary cartridge in the tail of the mortar bomb and incorporated a firing pin which, when the bomb was dropped onto the firing stud, then acted on the percussion cap of the primary cartridge. Due to this design difference, ammunition for other 81mm mortars would not fire when drop loaded into the British mortar. The opposite also applied as British mortar bombs would not fire in other mortars.



Draoich
 
I think British rounds would still fire in other nation's tubes. Reason is the primary cartridge had the built in firing cap which initiated on impact with the flat firing stud in a British mortar and the central anvil would also be pressed into the cap if it were dropped onto a conventional firing pin.

If this were not the case, the British rounds would not work in barrels using the altered firing pin which could present a problem in the field.

Course the firing pin or firing stud can be easily changed out on a British 3-inch mortar. And likewise, the primary cartridges can have the built-in anvil cap removed and then be used like a normal cartridge in any other army.

On a related note, my live 3-inch mortar had a wartime dated firing stud in the ball when I got the mortar to restore and then reactivate. Since I had no source for the caps with built-in firing pin/anvils, I machined a new conventional firing pin for the mortar. That way I could load my own 12-gauge primary cartridges which use standard shotgun shell primers to initiate the powder charge. Did the same for my live 4.2-inch and that way I can use the same primary cartridges in both barrels. Less to remember when packing gear to go on a shoot.
 
horsa said:
On a related note, my live 3-inch mortar had a wartime dated firing stud in the ball when I got the mortar to restore and then reactivate. Since I had no source for the caps with built in firing pin/anvils, I machined a new conventional firing pin for the mortar. That way I could load my own 12-gauge primary cartridges which use standard shotgun shell primers to initiate the powder charge. Did the same for my live 4.2-inch and that way I can use the same primary cartridges in both barrels. Less to remember when packing gear to go on a shoot.
Click to expand...

Any chance of seeing some footage of your mortars being fired? Its something e can only dream about here in the UK:tinysmile_cry_t3:
Hangarman
 
[ame]http://www.youtube.com/watch?v=TshEHDD-GvQ[/ame]

I don't have much video of the various mortars being fired. The link above is a very short clip showing the 4.2-inch when I was first testing the welds on the barrel. It had four demilling torch cuts that had to be welded and polished up once I got federal approval to reactivate the barrel. They are the shiny spots visible in the video.



This test shot was also to see if the firing pins I had made would work with the cartridges I loaded. Base charge was pretty light at about 80 grains of Triple 7 which is a black powder substitute. The bomb only went about 75 yards with this light load. My normal primary charge is 150 grains for the 4.2-inch and then I can add raw powder down the barrel to serve as augmenting cartridges. You need to wait to make sure nothing is still burning in the barrel though or it would flash off as it was poured. Not as safe as loading augmenting cartridges but much easier and quicker for making adjustments in the field while firing.



Due to having to retrieve the bombs after firing, we use a field with a roughly 300 yard long straight dirt road for our range. And we keep the tube at a fairly steep angle. Allows for a hotter charge which has a great effect when fired. The rounds get more travel that way but stay where we can track them. And they are really moving fast with a full charge, compared to the clearly visible shot in the video clip.



I'll see if I can upload a couple of 2-inch mortar shots for reference as well. I don't think I have any video of the 3-inch being fired.
 
[ame]http://www.youtube.com/watch?v=NOyziNlIa50[/ame]

Found a video of the 3-inch barrel being proof tested after it had been reactivated. The shot has a hotter charge compared to the 4.2-inch video. I was only doing a couple of shots that day so didn't completely set up the mortar. You can see there is no recoil spring hooked up and I didn't bother to set the base plate flat on the ground.

Both of these mortars are cleaned up now. Didn't want to paint them until I'd verified the welds wouldn't crack under pressure.

Will see if I can also find some of the 2-inch shots to post on YouTube as well.
 
[ame]http://www.youtube.com/watch?v=YEgNhbHh6GE[/ame]

[ame]http://www.youtube.com/watch?v=YbXK5s3YsCE[/ame]

OK, links above are two short video clips showing the 2-Inch Mortar and a newly made mount for the earlier pattern mortar sight in action. First shows me trigger firing a 2-inch round. Second shot is my wife firing and I’m down range 200 yards training the kids how to be Olympic Javelin Catchers. You need to start out with small things like the 2-inch rounds though to really get good enough for the Olympics. If you turn your volume up, you can hear the round coming down in the second video clip. It landed about 15 yards away so obviously my wife needs a little more practice. :tinysmile_kiss_t4:


NOTE: Don't try this at home...
 
Last edited:
Stokes Brandt type firing pin

Hi,
Great videos and information. In response to Horsa's point about British mortar bombs probably firing in other mortar types, I think this is not possible. The British mortar bomb has fins which extend downwards below the base of the Primary cartridge. All the European mortars used the Brandt type mortar bomb or similar and the Stokes Brandt type firing pin would not be able to even touch the base of the British Primary cartridge as the fins would create a stand-off.
Regards,
Draoich
 
Thanks Horsa, How great to have not one but three mortars to play with! Never tried playing catch with a mortar though. Thanks for sharing .
Hangarman:tomato:
 
Hey Draoich, on the rounds and tubes during the war, I was speculating based on your initial post related to firing pins and firing studs. But just the opposite in thinking the British would be able to use foreign captured rounds in their own weapons if they adopted a conventional firing pin.

My 3-inch mortar had a wartime dated firing stud intended to work with primary cartridges like the example Racefiets posted an image of. I have a couple of those cartridges but no way to produce the clip-on firing pin/anvil device attached to them. So that was why I built my own conventional firing pin to work with normal 12-gauge cartridges and plain primers.

Living Free in Texas....for now....no telling how much longer we can hold out :ridinghorse:
 
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