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

 

 

 

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 Jackís 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, thatís 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 ďUĒ 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 Ĺ 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 didnít 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 wonít 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.