British 4.2-inch Heavy Mortar

[Keith Brooker]

Had to have some one with me from the museum so that i did not take it home. i do have a VHS film 120 Mortar Battery 61st Light Regiment Royal Artillery in Korea 1951 - 1953 towing them with Morris C8 GS and firing them some of it in colour.

[Neil Ashley]

Did we ever decide if this late war version ever actually saw any war-time service?

[horsa]

Hey Keith,

I've got one of the towed mortars that I am just starting to restore. Haven't seen any for sale but people still say there might be one or two available in Australia. Will post something if I hear anything on one being available.

One thing that I will need to fabricate is the pair of poles used to help swing the wheels up and down for lowering the base. I'd guess they are 2" diameter since the sockets in the base and wheel brackets are slightly bigger than that. And the length is probably 40-42" based on how it seems to be the same rough length of the base plate. It would help me in getting something made proper to know a few true measuements if you have access to the example at your museum since it has them with it. Items related that I can think of are:

Diameter of socket end of pole.
Diameter of the blocking wide part of the pole (ring about 1" tall?).
Diameter of the hand holding end of the pole.
Length of the thinner hand holding end of the pole.
Length from wide end of pole to the blocking ring.
Overall length of the entire pole.
And are they hollow, made of sections of pipe welded together or are they solid and milled down? Seems it would be entirely too heavy if solid.

Many thanks in advance.

[Keith Brooker]

Hi David,
The last time i was down there was 1 1/2 years ago, might be worth giveing them a email as they are very helpfull . www.firepower.org.uk thats the Woolwich firepower museum. I can inlarge my photos if thats any help. photo of Morris C8 GS 15Cwt trucks with Mortar positions of A Troop, 170 Light Battery, 1 RNF & 1 RUR just prior to withdrawl from the Imjin area Korea 1951. [ Brigadier M N S McCord ]

[horsa]

I'll make contact with the museum and see if they can take measurments. Appreciate the link to their web site.

Your photo shows how amazing the support logistics had to be. I've read accounts from six years earlier during the fighting in the Netherlands where the 4.2" mortar platoon would fire off 3000 rounds during an offensive. Hard to imagine what it would take to transport in that many rounds.

[wally2960]

Hello, recently I bought a mortarmounting and the seller told me that it was of the 4.2". After compairing it with the 1944 pictures of the 2 Kensington ( 49th West Riding ID) taken in Belgium, and already posted on this topic I can't find any difference between the mounting shown on the picture and the one I've bought. But strangely the only marking I found are showing: 1942, MTG 3 Inch Mor.
Is this normal? Thanks Wally

[horsa]

Shot below for reference shows three mounts with the first being for the 3-inch mortar, middle one is for the lightened 4.2-inch mortar and the third one being for the towed 4.2-inch mortar.

The lightened version would appear to be based on the standard 3-inch format with the addition of a third leg, third leg locking bar which might not be visible in the shot and of course the cradle for the larger 4.2-inch barrel. Worm gear seems to be the same on each of them. There are differences in the locks for the standard legs on both mounts but I think that is a difference found in early and late 3-inch mounts and not something to differentiate the 3-inch vs 4.2-inch patterns.



Nomenclature is not official as I don't have a manual handy so hope you can decipher what I'm calling things in this post.

[wally2960]

Thank you David, for the information. Here is a picture of my tripod and I believe it is a different version of the lightened version in the middle of the shot. Now I'm started cleaning it and to remove all the rust and red paint. I found some markings refering to the manufacturer. It seems that it was built by J.C.L. in 1942 and broad arrow.
For the restauration I search exact mesurements for the barrel because the possibility of finding an original barrel will be very small, so I want to make a replacement but therefore I need the length of the barrel. greetings Wally

here the link to pictures

http://brechtsoorlogsmuseum.freeforu...-inch-t12.html

[horsa]

That mounting in the center is one I borrowed for comparison to my others in the shot so I don't know it's history. But it is marked 4.2 and has the Australian D/|\D markings on it with a 1943 date. I'd say the one you posted is virtually identical though. Could be yours was an earlier produced 3" mount that was modified to the 4.2" format as those bigger mortars were coming on-line since it has a 1942 date.

For the barrel, the length of the smooth bore pipe is 60 inches with a muzzle outside diameter of 4.75 inches. The first 18 inches from the breech end has an outside diameter of 5 inches.

[wally2960]

Thanks for the detailed mesuraments and the quick reply. I have another question concerning my restaurationproject: which kind of sighting were put on the mortar? After some detailed examination of the wartime photo's I can't see much difference with the 3 Inch mortar sights. Was it common to put 3 Inch optics on the 4.2 inch mortar? greetings Wally

[horsa]

There were two main types of sights used and after the 4.2" mortars got into general issue, it seems they changed the data plates on them to read something along the lines of 3" and 4.2" mortar. The biggest visual difference on the two patterns is how they connect onto the mortar mount. One type has a socket and the other type has a dovetail. In the shot I previously posted showing some mounts, the center one uses a socket type sight and the other two have dovetail mounts.

I can try and get photos of both patterns sometime over the weekend if you need them.

[wally2960]

Hey David, I would be very interested in some pictures of the correct mortar sights used for the 4.2. It seems that my mount was equiped with a cradle of the socket type. Unfoutunatly the socket have been broken off since warend. While cleaning I noticed on the cradle two bolts near the outher edge of the cradle, not far from the socket. They also are present on the wartime picture placed on my forum. Do you know of what use they were? I've posted also new pictures of the cradle (with visible bolts).

http://brechtsoorlogsmuseum.freeforu...-inch-t12.html

[horsa]

Shots of the two basic types of sights used during the war. One on the left has the dovetail and the one on the right has a socket mount. Your mortar mounting used the socket type.





The bolts you were talking about are hard to figure out from the angle. With the cradle and sight adjustment area being incomplete, it could be that someone added bolts to fill the holes.

[horsa]

I've been slowly restoring a 4.2" mortar and finally managed to get some firing pins turned down from stainless steel round bar stock. Originals were firing studs as the launching cartridges each had their own firing pin in a clip attached to the cartridge so they were self contained for launching. Guess that eliminated the chance of a malfunction in the field due to a firing pin breaking or wearing down.

I wanted to load my own cartridges from 12-gauge shotgun shell hulls and prefer a fixed firing pin so the rounds light off on impact with the pin at the bottom of the tube. Plus I have no way of producing self contained caps like they had during the war.

Took my live barrel out over the weekend and used a normal infantry base and legs which I am storing for someone else since my base and legs are the towed pattern which is much larger and harder to mess with for just a few test shots.

Link below is a very short YouTube video showing a single launch of an original round using black powder. I only used enough to throw the round out 225 yards which is extremely short range compared to the wartime maximum ranges of 3500 yards. As such, the round is moving fairly slow so you can see it leave the tube. I also didn't dig in the base since I was using light loads.

http://www.youtube.com/watch?v=TshEHDD-GvQ

Figured it would be OK to add this to the existing message thread since its one of the types of mortars being discussed. And in case anyone is wondering, its a BATF approved destructive device here in the USA so I can legally take it out and get it dirty now and then

[alleramilitaria]

whats the range?

[horsa]

Hey Dave,

Mentioned the range in the first post....I was using only enough powder to get the rounds out about 225 yards. There is an old shack with overgrown trees around it in the field I was shooting from and it sits 150 yards from where I set up. Rounds were soaring over it before arcing back towards the ground. There was roughly a 15mph headwind I was shooting into and the rounds had no impact fuzes which left a 1.75" hole in the ends. Not very aerodynamic conditions so the same powder charge would probably get further range with calm conditions and thick tape over the holes. And more powder would easily toss them further but then there would be the issue of finding them.

With high angle and a reduced charge, we could easily set up the towed mortar and do a demonstration firing at Mullin's place next year. Probably have to do it for the vehicle owners and reenactors though as opposed to when the public is there due to liability.

Next time I head south for testing I'll have someone else along to take pictures and will be prepared with more rounds and power to experiment with. The video I posted was shot from my little digital camera being placed on the back of the pickup bed.

[lssah2025]

That's awesome Dave, still working out the details on my 3", think I found someone to do up my baseplates, Thanks again for the dimensions, also I was thinking of doing up a DD/mortar tube, are the firing pins the same as you made for the 4.2"? Or would I need to do something different? Looks like the Humber and Trailer will be here by the end of the year, if not Jan. 2010 when I get back on leave from the sandbox. Also I picked up a lot of 19 set stuff, so if you need anything for your carrier let me know.

[horsa]

Hey Lance,

I had an original 1942 dated 3" mortar firing stud. Problem is you need launching cartridges which have the caps with individual firing pins build into them. When the round is dropped down the tube, the stud is the stop against the center of the cartridge and it compessed the build in firing pin into the primer. I took the specs from the orignial and made actual firing pins which will work without the WWII style cartridges. That way you can use modern plastic 12-gauge shotgun shell hulls and load them with black powder or modern substitute.

I'll try and get photos posted in the next day or two of the 3" and 4.2" versions I made for my tubes along with an example of the WWII style cartridges with a firing stud for reference.

[lssah2025]

Excellent, that is what I am looking for, I might just do up one of the trap door mortar tubes for public displays etc, drop down the round with a 12 ga charge, big puff of smoke and pull the round out the bottom...I picked up 3 complete 19 sets for tank installation with all goodies so I have some spare stuff, also my 22 set is in and I worked on it the last time I was home on leave. I also picked up a complete ranging set with base which will be coming over in the container, same base as the 22 set to mount it in a vehicle, so I can install it in my A/B jeep. I also picked up an original wooden battery box for 10 volt that I will have to get you some pics of, looks like same dimensions as the 6 volt, plus 2 metal battery carriers 50's dated with original 6 volt batteries, so more pics there..OK patiently awaiting the mortar stuff....

[horsa]

Attached are two shots showing original and my homemade versions of firing pins/studs. I'm not sure what the British equivalent thread size is but both mortar balls that I have would accept a 5/8" coarse thread bolt. The original firing stud was 7/8" diameter so I used that for my homemade firing pins. The other shot has my original 3” firing stud along with two wartime demilled launching cartridges. One has the self contained firing pin in place and the other shows it in parts for comparison. Not something I could readily reproduce which is why I went back to a more traditional weapon firing pin using simple standard primed cartridges.

Material I used is 7/8" diameter stainless steel. The 3" firing pin is 3.25" long and the 4.2" firing pin is 4.5" long. Each of these measurements includes the 5/8" threaded section. To make the pin itself, drill a hole in the center of the face and tap in a short length of 3/32" round stock spring steel or you can use the shaft from a drill bit of the same diameter.

So far I haven't had a failure on any of my self loaded launching cartridges that I've test fired. I'm using 12-gauge hulls which I use a roll crimper to seal after filling. Powder is two F (FFG) Triple Seven by Hodgdon which is a clean modern black powder substitute. It burns dirty and greasy like black powder but cleans up easily with water. This is the same powder I've been using with my 2" mortar. I've tried several types of smokeless powder that burned really clean but they don't produce a satisfactory amount of lift for the volume of powder. Probably 1/6th the range at best compared with an equivalent load of 777 powder.

For augmenting cartridges, I planned to fill paper quarter rolls with powder and rubber band them to the fins which is similar to the wartime method where they used celluloid tubes held in place by springs. But while experimenting, I found you can simply pour the added powder charge down the barrel and it cooks off perfectly when the normal launching cartridge hits the firing pin and sets of the main charge.

[wally2960]

Last week I've bought another 4.2 inch mortar mounting from someone who offered it to me because he knew that I'm working on a restauration of this mortar. But now I want to trade it to other parts of the mortar such as the tube or the baseplate.

The mounting is fabricated by JCL and is dated 1942. It also has the broad arrow and all parts are functional.

Please let me know if you are interested

http://brechtsoorlogsmuseum.freeforu...-inch-t12.html