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Build your own Bren Gun! Part 1--getting started: full-autos cost as much as a luxury car, and even semi-autos aren't cheap. But if you have $350, a good set of tools, about 100 hours work time and a lot of patience and ingenuity, you can have your own semi-auto Bren.

The Bren light machine gun was fielded by the British and Commonwealth forces from just before World War II until as late as the Persian Gulf War.

Many military firearms authorities like SGN's own Peter Kokalis consider it the finest magazine-fed light machine gun ever made.

I have wanted a Bren for my collection of military arms for many years. There are NFA registered and transferable examples, but at today's highly inflated legal machine gun prices they are out of the reach of most blue collar working class stiffs like me, as they can run up to $50,000.

Much cheaper is a semi-auto replica of the Bren. There are several small manufacturers making them, but even those can run $2,500+. This price is fine for those with a fair amount of discretionary income, but not for those of us who have been hit hard by the current economy.

I lost my 33-year industrial job during the economic downturn, and health issues have made it hard to find new high-paying employment. I'm sure there are many SGN readers who are as financially challenged as I am. There is just no way we can drop $2,500 for a new toy.

There is one last low-cost option for some resourceful readers: home-build a semi-auto version. It may be hard to believe, based on retail prices of manufactured Brens, but you can build a semi-auto Bren for about $350. Of course, this low-cost option does have some big conditions. You have to do all the work yourself. If you buy the required U.S.-made parts and semi-auto parts, the price will escalate quickly. If you have to pay others for their labor, the cost will also go up fast.

This project is very labor-intensive, but material cost is extremely low. Any hobbyist gunsmith with a small hobby machine shop should be able to complete the project under the quoted $350 cost. A milling machine, metal lathe, MIG welder, bandsaw, torch and a few metalworking hand tools are required to complete it.

You can get by without some of the machine tools if you have the skill and endurance for a lot of tedious hand work. With the major machine tools, you can expect to put about 100 hours into this project. I had many more hours involved, but most of my time was engineering the project and testing concepts that I came up with (including many that didn't pan out!).

Any time you build a semi-auto firearm based on a foreign full-auto, there are legal issues to take into consideration. U.S. law and BATFE regulations forbid building a full-auto Bren gun. Since 1986, the BATFE has prohibited the manufacture of new full-auto guns for private individuals.


Illegally building or possessing an unregistered full-auto firearm is punishable by a $10,000 fine and a prison sentence of up to 10 years in a Federal penitentiary. One of my coworkers had a son who thought this law didn't apply to him, and he spent a few years in the pen when it became well known that he had illegal machine guns.


Take this advice to heart, build only legal semi-auto guns! Semi-auto versions of many full-auto guns are legal but they must not be "readily restorable" to machine gun status. If a gun is considered by the BATFE to be "readily restorable" to machine gun status, it makes no difference if it only functions as semi-auto, it is still in their eyes a machine gun, and therefore illegal.

The BATFE has in the past issued what is known in the gun business as approval letters for semi-auto Bren designs. These letters state that if a gun is built in a certain way, it is considered to be a legal semi-automatic firearm rather than an illegal full-auto. These letters have been issued to small manufacturers and individuals.

Copies of these approval letters can be found on several semi-auto Bren building websites. While there are several letters and designs posted on the internet, all of them feature certain design parameters for the legal construction of a semi-auto Bren. One can also contact the firearms technology branch of the BATFE and seek technical advice concerning legal methods to building a semi-auto Bren.

The most common and economical way of making a semi-auto Bren receiver is to use the pieces of a properly destroyed Bren LMG receiver. This destroyed receiver has to have been torch-cut to BATFE specifications. To be legal under BATFE regulations, the reconstructed receiver must be made so it cannot accept several original full-auto Bren internal parts.

It should be noted that at no time during reconstruction can the receiver ever be in machine gun configuration, not even for five minutes! As the receiver sections are being reconnected by welding, they must always be in semi-auto only configuration. You cannot reconstruct a full-auto receiver, then convert it to semi-auto; to do so would be illegal. This is a vitally important point that must be observed. When we get to receiver construction, these issues will be talked about in more depth.

Besides not allowing certain unmodified full-auto parts in the receiver, several Bren parts need to be modified to semi-auto only configuration. The bolt, bolt carrier, lower receiver and fire control group will need to be modified to semi-auto only configuration. These modifications should be done before making the receiver, so there is no doubt that you are working on a semi-auto project.

Having a completed semi-auto receiver plus unmodified full-auto internal parts could be a touchy legal issue, since the full-auto parts could conceivably be modified to fit the semi receiver and create full-auto fire out of a semi receiver.

To be legal, the basic operating system of the Bren must be changed. The Bren is an open-bolt design and the BATFE has ruled in the past that open bolt operation is purely a machine gun feature, and therefore not legal for semi-auto guns. The operating system of the new semi-auto Bren must be changed to closed-bolt operation. This will require making several new parts and modifying several old ones.

One last legal concern is about what is known as U.S. compliance or 922r compliance. Several years ago firearms laws were changed to prevent the importation of certain semi-auto military-style firearms. The law also specified that these firearms could not be assembled in the U.S. with more than 10 foreign parts out of a published list of 20 specified parts.

In a nutshell, the law says that certain firearms such as this project cannot have more than 10 of the listed foreign parts. 10 or fewer is legal but more than 10 is illegal. 10 or fewer parts make it a legal U.S.-made firearm, more than 10 make it an illegal imported gun.

In this article, several foreign-made parts will be replaced by self-made U.S. parts. Some of these U.S.-made parts can be purchased from semi-auto Bren parts suppliers, but if you make them in your own workshop, they are inexpensive and certainly U.S.-made.

This project comes in right at the limit. It has 10 of the specified foreign parts. Since the law says 10 or fewer, this project is a legal U.S.-made gun. Do not delete some of these U.S. parts, because that would put the parts count over 10 and change the legal status of the project.


The first thing you need for this project is a military surplus Bren parts set. Most of these parts sets include all parts for a Bren minus the barrel. A destroyed Bren receiver is normally included.

These receivers have been torch cut to BATFE specifications, and are now considered nothing more than scrap metal. Under federal law, these parts sets are unrestricted, but check your local and state laws. Bren parts kits are available from several SGN advertisers at several prices.

I frequent a web site known as that is a website for firearms builders. Weaponeer had made arrangements with Military Gun Supply of Ft. Worth, Texas to offer discounted Bren kits through the Weaponeer site. These kits were offered for $185 plus shipping.

Since these were so inexpensive, I ordered two of them. While you can get by with one parts set, I wanted one for a semi-auto gun and another for a non-functional display gun. Since the dummy gun wouldn't have any internal parts, the leftovers could be used for the semi project if needed. Having extra parts on hand is convenient if you mess up a part when modifying it and need a replacement.

The parts kits I received were in pretty good shape. They showed a lot of finish wear but were functionally fine. Just keep in mind you are buying 65-year-old used parts and they aren't going to look new. All parts for this project will eventually be refinished, so finish condition is unimportant; all that matters is that they are functional.


These parts sets came without the barrels. Fortunately, Bren barrels are available and very inexpensive right now. I bought two barrels since I had two projects. I ordered a new-condition barrel from Omega Weapons Systems for $75. When I received it, the barrel was just as advertised; it looked like it had been made yesterday.

The other barrel I ordered was slightly cheaper, since it was going to go on a dummy gun. SGN advertiser I.O. Inc., of Monroe N.C., had what was advertised as good condition Bren barrels for $59. What I received from I.O. Inc. was still in pretty decent shape, even though it was less expensive. It showed a fair amount of finish wear, but the bore was very good. Either barrel would be fine for this project.


Neither of my parts kits came with magazines. Fortunately, Bren mags are very inexpensive. I got my magazines from I.O. Inc. These magazines were only $48 for 12 magazines or $6 each for singles. This is a real bargain for military grade 30-round magazines. My research also found them at similar prices at Numrich Gun Parts and Omega Weapons Systems.


This project will require some materials for parts fabrication, namely springs, 4130 steel tubing, 4140 bar stock and a few other miscellaneous pieces of steel. These needs will be addressed as the parts are made.


Before I start describing how I made this project, a couple things need to be made perfectly clear to those who are considering doing one. This article is only a rough description of how I built this project. I am not a professional gunsmith or firearms engineer. I am simply a hobbyist who is sharing my building experiences with others.

While this article can be used as a very rough guide, it does not contain all the information one needs to complete this project. Anyone using this article to help in building this project will have to supplement this information with his own gunsmithing skills and knowledge.

This project is advanced hobby gunsmithing and requires extensive metalworking skills and firearms knowledge. Many parts, especially the receiver, must be fabricated with excellent workmanship to function safely and correctly.

You must completely understand how a Bren gun operates. You should do considerable research on how a Bren gun functions. Reference materials on Bren gun operation such as Small Arms of the World by Smith and Smith or an older edition of Jane's Infantry Weapons should be consulted, along with Peter Kokalis' article in SGN (9/20/07).

You need significant gunsmithing knowledge to determine if the self-made parts fit and function correctly. I cannot overstate this: this project is not simple kit building, it is making a gun and parts. I will only be giving some general dimensions for the parts being made in this project since parts fit will vary somewhat between individual guns and also depend on the skill of the builder.

It is up to the potential builder to determine if the parts are correct and function properly. You are the builder, I'm just showing what worked for me; your results may be different.

Neither SGN nor the author accept any responsibility for the safety or legality of this project. The builder/reader is totally responsible for his own project. If you choose to do this project you and only you are responsible for the results.

If you have the skill and patience, however, you'll find this a fascinating and challenging project requiring little cash but a lot of ingenuity.

Next month (8120 issue): Making the compliance parts.
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Author:Matthews, Steven
Publication:Shotgun News
Geographic Code:1USA
Date:Jul 20, 2010
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