Long Range Desert Group Photos (Equipment)

The Manufacturing of a Boys Anti Tank Rifle Gas Gun

By Kim Calvert

At the time I was machining the Vickers K guns I was also working on converting the Breda M37 into a gas gun. At that time my vision was a little one sided. I really did not think too much about making the Vickers into a gas gun; I was already making one, the Breda.

If I had it to do all over again I would have spent the extra time and money right from the start. The K guns I did make are based on real dimensions and some of the dimensions I would need to fudge a little to make everything fit so it’s too late to modify the ones I did make. I decided right from the start that the new project would be a gas gun no matter which piece of history I choose. So that left me thinking. I had a great time designing and building the Vickers. The Breda was a privilege to work on, what little project could I do next?

I started looking at photos from my many books on the LRDG and SAS for some ideas. The thought of building a Lewis gun really was taunting me, after all who wouldn’t want a Lewis gun right? However there was one gun that really intrigued me and can be seen in many photos both mounted and used on its Mono-Pod, the Boys Anti Tank Rifle. Not only does it look awesome in its simplistic design but the fact that you see them mounted on LRDG trucks and used by infantry as well really got me. I started thinking; at most events we will probably have more troopers than we can fit in to a couple of jeeps and the truck. Such was the case in April 2010 at the Battle of Tunisia re-enactment and again at MTH. If that is the case then Troopers could have a lot of fun setting up and firing the B.A.T.R. at the enemy from a set position while waiting their turn to go on patrol during a battle reenactment. It can also give us more noise making fire power for the truck. However we would eventually use it did not matter too me the Boys it was.

I began as I always do with a lot of research. There are some pretty good reasons why this gun was considered obsolete before the start of the war. The gun was 64 inches long and weighed 35 pounds, it was big and heavy. The recoil could tear your arm off.

It used a 5 round clip and the bore was .55. It was incredibly slow to load and fire. In fact it fired 10 rounds per minute according to the manual. By the time World War Two broke out the gun was all but useless except against some armored cars and knocking holes in walls of buildings. Even though this weapon was considered obsolete before 1940 it saw use until 1944 on all fronts of the war.

This project started out on a high note as I discovered much information on the gun as well as photos, sketches, mechanical drawings with at least some dimensions. I also had a 1/35^th scale model of the Boys from a model kit I was working on. I took my calipers and scaled some of the dimensions up using the model as a guide. As it was molded in plastic and looked a little heavy, I subtracted .005 of an inch from any dimensions I took from the model and multiplied by that number.

Jack had an original 5 round clip he donated to the project and having that one piece of the real gun allowed me to verify and figure out even more dimensions. I started looking around for some more real parts and at Numrich gun parts they had many bits and pieces for the Boys. I was able to purchase a real trigger, the wooden pistol grip at the trigger area a clip lock. Finding and purchasing the wooden grip was icing on the cake as I did not want to have to turn one on the lathe. A lot of work went into making that grip back in 1937.

As written in other reports I used my C.A.M. system and C.N.C (as well as manual) machines to get the job done. Making this gun would require a lot of C.N.C. milling. The barrel which is 36 inches long would need to be turned on the lathe and hollow. As I saw far more issues with the manufacturing of the barrel I started there.

The barrel would be made with 6 separate parts. The muzzle flash, the main length and taper of the barrel (2 pieces) then the 3 larger pieces that lead to the receiver. I had to use a 12 .0 long .532 diameter drill and drill from both sides of both pieces to drill the center of the barrel. It wasn’t easy. I did all the lathe pieces using the C.N.C. lathe. It took about 10 hours to program and machine the 6 parts used for the barrel.

Next I started on the bottom portion of the receiver. This would really be nothing more than a 1.5 + 3.0 + 24.0 piece of aluminum. I machined the inside channel, several pockets or windows through the thickness of the part and drilled holes in each end in preparation for the 2 end caps. I then milled the first end cap which holds the barrel to the receiver. This one piece will hold the barrel on its center line so I can line up the next piece of the receiver.

Machining the top part of the receiver would require a lot of mill work. Not only do I need to mill the outside periphery but the inside would need to be hollow to except the gas gun components. Milling the outside contours was really easy and this is because of the simplistic design of the receiver. After the contours were milled I turned the part over and cleared out the inside. It is an unfortunate but necessary waste of material as the solid inside turns into aluminum chips. The original gun is made of tool steel so many parts were welded together. I do not have the luxury of a Tig welder so my model shows a few more screws than the original. The large diameter of the barrel where it meets the receiver is bolted from the bottom of the receiver into the large diameter using a 3/8-16 bolt. Then there are 2, 3/8 pins holding the rest of the barrel at the end cap. The result is a very hardy assembly for the barrel. The top part of the receiver is then bolted using ¼-20 bolts through the bottom of the receiver and into the top section. All these bolts are counter board as not to see them.

The shoulder piece with handle and pad was a good challenge. I started out with a big chunk of aluminum; mill the features on one side, turn the block over and mill the features on the opposite side and the big radius for the shoulder area. I then machined the matching radius to affix the thick leather padding to. When that was done I shipped that part off to Trooper Bill I. who created and installed the leather padding. Thanks Bill!!!

I really did not have much to go by as far as dimensions were concerned for the shoulder piece. As a result I made one mistake. The angle that the hand grip is machined to is not correct. I created a sharper angle. If you compare the original to mine you can see it right away. Unfortunately fixing this means another expensive piece of material and few more hours of machining so this proto type will remain. I fixed that part of the program and if I machine another one the problem is solved. For now and until I can find an original I used a wooden Bren barrel grip for the butt handle. If I cannot find the original I will dig out my wood lathe and turn one but right now this will do.

As I mentioned I was able to find an unissued wooden trigger grip at Numrich. Just as with the real magazine I was able to machine the trigger area using the real grip as a size reference to the rest of the gun. Machining this part was a matter of milling the shape of the periphery, milling one side to thickness turning it over and removing the rest of the material to the desired thickness.

I have the original trigger components which are wired with a spring so it has some tension and spring back against the electric switch.

The Gas Gun Components:

I ordered the two solenoids and PLC from my usual source however as this is a single shot rifle I opted for a PLC which is normally installed for gas operated cannon. It simply has a slower fill time so it forces you to wait longer between shots. This will get us closer (although not exact) to the real firing rate of the original Boys. The 2 solenoids, mixing chamber, spark plug are all installed inside the hollowed out receiver.

Now some artistic license and imagination will be needed. This gun fires from a 5 round clip, not a belt or round drum or from any other means. It is always difficult and really almost impossible to hide all the wires and hoses that are required to operate the gas gun. I found a couple of photos of a wooden Boys Bandolier box which I fudged the dimensions on to accommodate the 12 volt battery, coil, PLC (with on and off switch) on one side of the box, I then partitioned the box to mount the oxy/propane tanks, regulators and hoses. Now all the electric wires, hoses etc come out the back of the box and fit into a canvas sock which leads right to the bottom of the receiver. If the gun is used with its mono pod at a stationary position we can bury the sock in the dirt and for the most part it will not be visible. If we use it in the back of the truck it will have to hang but as far as I am concerned this breech in authenticity is acceptable. This leads me to something very important. When your system is complete and you open the valves on the oxygen and propane for the first time before you try to fire your gun take the time to mix up some soap and water and glob it on at any gas fitting. Right away you can see if you have any leaks by watching the water bubble and move from the leaking area. If you see this STOP something is not tight and you have the potential for unwanted explosion. Further more periodic checking (especially after a battle) of all fittings is necessary to insure safe handling.

As this gun will be really loud and I don’t wish to make my neighbors or the local authorities any more jumpy than they already are I will not test fire the gun until the desert battle in September.

As far as putting some color into the gun I will paint it. I have heard from several of you in regards to making paint stick or even scratch resistant on aluminum. Well there is no such thing as complete scratch resistance however here is a good system to get close to scratch proof.

I start out by cleaning all aluminum parts in the sink with hot water and liquid dish soap. Wash with a wash cloth of some kind getting off all dirt and grease, towel dry with lint free cloth or blow dry. Let the parts dry completely. Next clean the metal with acetone. Make sure its acetone as it evaporates and leaves no residue. Next I use Krylon 2 times the coverage gray primer. I paint on 2 coats letting each coat dry for about an hour. Then I use Krylon 2 times the coverage Flat Black. I spray 2 or 3 coats making sure I have painted every area. I then let this dry over night. Now if you have an air brush you can mix up some dark gray paint and use it to do some panel fade as well as spraying a mist coat over the entire gun. This starts to give the gun an aged look. I then mix up some dark rusty brown color I over spray this color in specific areas. It gives a patina type look to the metal. When all this is dry 24 hours I spray Polyurathane Satin clear coat. I may spray 2 or 3 coats over the entire gun. This is what gives the paint a protective shell and instead of a dead flat finish it is satin which looks more gun like in 1 to 1 scale. When dry, rub your finger nail across the metal parts you will see a dull rub mark but not a scratch. If handled with some moderate care this paint should last a long time. To finish off the look of the gun I will take a piece of sand paper and actually remove some paint back down the shinny metal on sharp edges, any where there would be metal to metal movement and the usual wear and tear places. This gives the gun a real and warn look.

Well I don’t know about you guys but I am darn happy with the results. The gun looks very close in shape, form and size to the real thing. It will be a nice addition to our group.

I don’t know, I must be sick or something. As nice as this came out I still can’t get that Lewis gun out of my head. I believe my wife is 100% correct when she says I am like a Mad Scientist working in some dark laboratory some where like a disturbed individual as she frames it.

& I make no apologies, sometimes being disturbed is a good thing.

Kim

Breda M.G. Part 2
Making a gas operated non gun

If you will all re-call. At the end of the first Breda report I mentioned that we decided to convert the Breda M.G. into a gas gun. /span>

I am no gun smith so actually getting the Breda into blank firing condition was not an option as I am sure you would not find any gun smith in California who could legally put it back together to fire blanks. The law is really fuzzy when it comes to re-building De-milled weapons depending on who you talk too. Not only that but blanks are very expensive and getting harder to come by in California.

Converting it to a gas gun became the only intelligent option for me.

I began by doing some research in to how exactly these non-guns work There are several system variations but really they all work and do the same thing.

To begin with you need the proper solenoids and PLC. These are available and come all 3 pieces in a kit. When ordering I was asked what the specific rate of fire for the M37 was. The answer is 7 rounds per second. The PLC which controls the timing and rate of fire is then set to time the solenoids to fire at that rate each time the trigger is pushed. The 2 solenoids are installed on a piece of aluminum or steel that is machined to fit inside the receiver. You then need to machine an aluminum block to house the fittings that are used as gas jets. A spark plug is then installed at the front of this block. The block is installed in front of the solenoids on its machined platform and mounted inside the receiver. At the other end of the aluminum block is a fitting that holds a ¼ inch copper tube. This tube runs down the barrel of the Breda . Also inside the receiver you will see electrical wires, flexible metal tubing and a few different hydraulic/air type fittings.

Two holes are drilled in the bottom of the receiver to mount the fittings for the welding hose. Those fittings go into the receiver and into the machined aluminum block that houses the spark plug and gas jets. Inside the aluminum block is where the oxy/propane mix.

I drilled a 1 ¼ dia. hole through the cowling on the jeep under the M.G. mount and into the glove box. The wiring harness, ground wire and gas lines run down the mount into the glove box where the PLC, on/off switch and 12 v motorcycle coil are located.

I also drilled the same 1 ¼ dia. hole through the bottom of the glove box so that the electrical wire and gas lines could come through the bottom of the glove box and proceed under the passenger seat. From there the lines go to the rear of the jeep. I used the original wooden box that the Breda anti aircraft extension bi pod came in and permanently mounted it to the inside back of the cargo area of the jeep. It is just big enough to store the oxygen and propane tanks and regulators. Next to that box I installed a Breda ammo box to store the 12v motorcycle battery. This is the electrical source for the system. You could mount it to the battery in the jeep but only if you are converted to 12v which my jeep is not.

So here is a list of the major components used in the making of my gas gun.

An M.G. either from the de-milled condition or an aluminum or steel dummy.
The solenoids and PLC which are offered by several small internet companies. $175.00
A 12 volt motorcycle battery or gel cell battery.$50.00 to $100
A 12 volt coil. $50.00
Spark plug. $10.00
Spark plug wire $10.00
electric trigger switch $15.00
Off and on switch $5.00
Welding tanks and regulators: This I bought new at home depot. It is a small home use welding set which includes everything you need. Oxygen tank, 2 regulators, welding hose and fittings. You do not use the acetylene tank. This tank is replaced by a $5.00 bottle of propane just like you use for the newer camping stoves. The reason I bought new is I wanted the hoses and regulators to be new as not to have any leakage problems. This unit cost $300.00 but you can sell the other tank and the torch parts and recoup some of the money.

There are other odds and ends and I am sure I am forgetting something but these are the basic requirements.

Adjusting the regulators to get the right mix to produce the right sound and flash is tricky. It took me a while to figure out that my system/gun takes very little oxygen and barely any propane. I can get a loud bang out of it as well as some good muzzle flash.

The entire Breda project has taken the better part of a year working on it when I can but in the end it was all worth it. My next project may be a gas Bren gun. This will be more difficult than the Breda . The narrower and smaller the receiver is the more difficult it becomes. This is why a 50 cal or 30 cal or Vickers .303 is a great choice for a gas gun; they have an abundance of room.

My SAS jeep is now fully ready to go into battle with guns blazing and the only reoccurring cost is a $5.00 bottle of propane and $10.00 worth of welding oxygen.

Not bad compared to $100.00 or more for blanks for a full days battle.

Kim

Re-building the Breda M37
(into Propane firing Gas Non-gun, keeping it de-milled)

By Kim Calvert

The last time we all met (some of us for the first time) at Our October Marching Through History event. Jack had told me he brought a project for me to work on. Through e-mails over the last year or so Jack learned that I was a Tool Maker- C.N.C. machinist and now Manufacturing Supervisor for a major Aero Space Fastener company. I had told him that I have been a machinist for 25 years now. Even through our e-mails I sensed a sparkle in Jack’s eyes. At that time I had no idea that I would get to work on such an outstanding project.

As our fantastic weekend was winding down Jack produced 3 wooden boxes with Italian writing on them. As we opened the boxes Jack was explaining that inside the largest of the 3 boxes was a Breda Modello 37 machine gun in a de-milled condition. Until that weekend I had no idea what de-milled meant but opening the big box was like opening a treasure box. There it was the receiver in 3 pieces looking like there had been an explosion inside the box ripping apart the components of the gun.

In the next box was a complete Tool Kit for the M.G. with many spare parts, oiler boxes, dozens of springs, 2 or 3 firing pins and ejectors. Along with all the wrenches, screwdrivers everything that was needed to put it all back together.

In the third and final box was a strange looking Tri Pod. (More on this later)

Jack asked me if I would or could put it back together for him. I jumped at the chance.

I took everything home and started doing research on the gun, tri- pod and the tool box.

The first thing I wanted to make sure of is that it was legal for me living in Orange County CA to even posses such a gun even in pieces, so my research started there. I made some phone calls to the ATF and found out that so far what I had was legal because in this condition it is considered a non gun.

De-milling is a process that is strictly regulated by law enforcement. The receiver must be flame cut in 3 exact locations removing at least 3/8 of an inch of material in the process. All other components were in mint condition.

I discovered that Jack had purchased this gun and all accessories from I.M.A. which is a re-enactors dream web-site that I am sure most if not all of you have seen.

I started looking on the internet for pictures, mechanical drawings, blueprints what ever I could find. Photos and sketches are abundant. Unfortunately I could not find any mechanical drawings for this M.G. so some artistic license would be needed because I really had no idea what the missing flame cut parts looked like.

The next order of business was to remove all the flame cut areas of the receiver. I used a special gun that we have at work to tell me what kind of material (metal) the gun was made with. You simply turn on the gun hold it to the metal surface and within 10 seconds it can tell you what kind of metal it was made from. In this case it was 4340 steel. A very mild form of tool steel. The metal had also been heat treated to a Rock Well hardness of 41. Pretty typical for this type of material. The problem is that once they started the flame cut operation the material was super heated which causes the metal to become even harder. At the flame cut area the R/C was 63, that’s hard and hard to machine. Solid carbide cutters called End Mills would be needed to cut away the welded, flame cut- heated area. The receiver pieces were difficult to clamp in a vice because of all the irregular shapes. (You need to set the parts flat, straight and parallel in the vice to insure straight cuts with the end mill in a milling machine). Once all 3 pieces were milled I then took them to the surface grinder to create a smooth, flat surface.

I then put the 3 pieces of the receiver together using the top of the receiver as a guide to hold all the milled pieces together. From there I was able to measure with Calipers the gaps that were left due to the flame cutting and re-machining process. One gap was .675 of an inch. Another was .875 and the other .950. Now I new the thicknesses of the replacement pieces I would need to machine. With the top of the receiver off and looking down on the receiver it looks kind of like the letter U, so I needed to machine 3 “U” shaped pieces that I am calling Bridges because that is exactly what they are. These pieces will bridge the gaps of the missing receiver. (See photos).

I found some scrap 4340 material in the Tool Room and went to work machining the bridges. These bridges I machined were left a little bigger in width and finished in thickness and height. The reason I left these pieces heavy (Bigger) is that once they are welded into place I want to be able to machine them down to the finished dimensions of the receiver.

Once these bridges were complete I started on the welding process.

First I did a lot of test fitting of all the parts. Putting the entire gun together with interior as well as exterior components. The first problem I saw was that the flame cutting process removed more than ½ the threads that the barrel screws into. I did not want to have to re-machine new threads so I was very concerned about the barrel not wanting to stay together. I was able to overcome that obstacle and the barrel stays on just fine. With the top cap of the receiver on and all parts clamped together using wood working clamps the receiver was one piece (as long as you didn’t bump it). I than began to tack weld each piece into position. Stopping to test fit pieces and check for interior movement. Some metal thicknesses were very thin and the last thing I wanted to do is blow a hole in the receiver using too much heat. When possible I cold welded as not to have that happen. I tried to run a penetrating full bead of weld around each piece as not to have too many ugly looking gaps and lines. I do not claim to be much of a welder so I must thank Don Warner for his help and assistance in the welding process. The most difficult part of this process so far was keeping it all lined up so that there would not be any big mismatches in the receiver. At this point what I did not realize was that due to the flame cutting process some of the receiver had warped so I new the finish maching would not be easy. With all pieces welded in place I began to re-machine the receiver. This proved to be difficult because the odd shape of the receiver made it very hard to indicate all surfaces flat and parallel which is important as not to have too much undercutting or leaving a bump of material here or there. Remember I mentioned Artistic License at the beginning of this report. Machining the welded pieces was pretty straight forward until the finish passes. I had done the best I could while indicating all the surfaces. Most areas were within + or - .010 but some were worse. All I could do was machine down to the original surface and try not to undercut the receiver. Once machining was complete I used a die grinder to smooth out any mismatches and hide the lines where the weld met the receiver. After this I used a finish sander to smooth over the marks left from the die grinder. Once that was all complete I bead blasted the entire surface of the receiver to give it a more uniform looking surface. Next I had to decide what type of finish (color) to use. Bluing would not look right against the rest of the 70+ year old gun. I decided to send it out for Black Oxide treatment. I won’t go into the process but when finished it would have a tough almost impossible to scratch black finish.

As you can see from the finished photos it looks pretty darn good.

All in all this was a great project for me to work on and I just want to say thanks to Jack for having faith that I could get it done.

About half way through this project we decided that we would create a Propane firing mechanism for this gun. That will be my next installment on this project.

Kim Calvert