This article may be copied and distributed freely with the following restrictions: No one may claim it as their own work, and no profit may be made off it without my knowledge and permission. Anyone wishing to use it as part of a Web Page may do so as long as the above restrictions are not violated and the restrictions are clearly stated in reference to them.

    For those of you who have never worked with brass before, a note of caution!! Drill bits and other cutting tools have a marked tendency to grab when working brass. Always have the pieces firmly clamped down, and always feed slowly. Do not attempt to drill out the 5/16 holes in this article with a drill bit!! If you do not have a lathe I also recommend against using the end mill. When I first tried to make a gun using a 5/16 drill bit, the drill grabbed the fitting and spun an unclamped 40 pound drill press vise around on the press table.

    If you have a steady hand and a large dose of masochism you can do all the steps with just a drill. However, to retain your sanity, you should have at least a small drill press. The drill press will quickly become invaluable for other projects once you have acquired one! A small (1/2 inch, 5 speed) drill press runs about $50-$100 from mail order tool places. A larger (5/8, 12 or 15 speed) drill press runs about $180-$250 from one of the mail order tool places like Harbor Freight. In addition Harbor Freight will pay for the shipping on any order over $50.

    Besides the drill press you need the following tools: some sort of vise for your drill press (preferably the type that has a way of adjusting the vise body position forwards or backwards and side to side while the base is clamped to the table), a good size file, a 3/16 drill bit or rod, and a Dremel 5/16 cylindrical cutting bit. I it is the larger of two that Dremel offers.

    If you plan to use the adjustable vise, or can afford a few more bucks, get a larger bench or floor drill press. The adjustable type vises run about $40-$50 and a plain vise $9-$40 from the same tool warehouses. If you get a small press try to get a 3 inch plain vise, the 4 inch vises are a little too large to clamp to the table.

    If you have a lathe, you are all set. With the lathe you can chuck a compression nut in the lathe and screw the fittings into it. For the lathe I recommend that you use a 5/16 inch end mill (it looks like a regular drill bit but has a flat end and four flutes, spiral things, rather than two), instead of the Dremel bit. Unfortunately, the right angle restrictors described later would be a pain to do on the lathe.

    You need at least one brass "T" fitting for each interrupter, and a fitting for each restrictor. For the restrictors you have a choice between two "flavors". The unions used to make the restrictor come in either straight or a 90 degree elbow. The advantage of the elbow fitting is that it takes up less space in the turret, because you do not need to curve the tube into the restrictor to make it level. The advantage of the straight fitting for those of you with a lathe is that you can screw it on just like the "T". The elbow is best made on the drill press.

    I recommend that you buy at least twice as many fittings as you need, to allow for waste and also so that you can make extras for future use. I also recommend that you make both types of restrictors. Having a choice may come in handy when installing the gun. For example the twin stern gun installation on my ship required one of each so that I could stagger the interrupter assemblies but still have the adjustment nut exposed.

    Although the piston should be made after the "T"s are bored out I will describe this process first, as it is the simplest. To make the piston the simplest method is to use a stainless steel nail. These are typically available at a marine supply store. Take a "T" fitting with you and get the size of nail whose shank is just a little too large to fit inside the "T" (the 3/16" portion). Buy several nails and/or prescreen them, and only use those whose heads are relatively round and true to the shank. An off-center head is almost impossible to properly file true. Cut off the end of the nail with the head on it making it longer than the "T" fitting (use a cut off wheel). Chuck the cut end into the drill press and file the ridges on the shank down so that it fits into the "T". At the same time square up the inner edge of the shank/head joint. Now file the edge of the nail until it will fit into the bored out portion of the "T" without binding.

    When filing the nail, hold the file by the end opposite the tang and hold it against the piece so that the file is being pulled away from you if it lacks a handle for the tang. This way if the file catches it will be thrown away from you. Get handles for your files, they only cost a couple of dollars for four or five. The files are much safer to use with them installed. Also have patience stainless steel is tough and the filling will go slow.

    You might also wish to invest in a cheap pair of dial calipers. A 6" dial caliper cost only $15 to $20 from places like Harbor Freight or Enco, and they come in handy for many measurements where a steel rule is just too course for the purpose. Alternately you could drill a 3/16" hole in a piece of metal and then cut and file a grove to the edge, and then use this to check the nail for proper diameter.

    To bore out the "T" fittings we first need to position them. Chuck a 3/16 straight rod or drill bit into the drill press. Lightly clamp a fitting in the vise using a compression nut on the clamped end, to protect the threads. Position the fitting/vise assembly on the table and clamp everything down with the rod inserted into the fitting. Do this with the drill press chuck run down so that you can later raise it to insert the cutter. This positions the fitting in line with the drill press shaft. This step is where the adjustable vise comes in handy, especially if you don't have twelve hands. You may be able to unscrew the fitting from the nut when done and just screw in the next fitting, but use the rod to check that the next fitting is still square. Remove the rod and insert the 5/16 cutter. Running the press at the lowest speed, slowly grind out the end of the fitting until you just hit the bottom of the old hole (see Figure 1). Cutting any further will likely weaken the fitting or even cut out through the bottom of the threaded area.

    Those of you with lathes can chuck a compression nut into the 3 jaw chuck and just screw the fitting into the nut. As each one is completed unscrew it and screw in the next one. You can also use the lathe to shape the piston from the SS nail, or make a piston from any metal you wish. I recommend SS though as the other corrosion proof metal brass tends to score and mushroom after a few years.

    The straight unions are made the same way as the "T"s. The elbows, however, are slightly different. The first thing you have to check on with the elbow is the internal machining. Check for any edges that might catch the BB and keep it from going through consistently (see Figure 2). Most of the elbows will have some kind of obstruction. The trick is to determine which end the BB can enter into and bounce off the obstruction without bouncing back down. After determining the end of the elbow the BB should enter, bore out the other end. The process is the same but each elbow will have to be clamped individually and probably can not be done productively on the lathe (no way to hold it in the 3 jaw chuck, a pain even in a 4 jaw).

    Now you need to make the bottom of the interrupter assembly (the nut that holds the piston in place). The easiest way is with a lathe. Chuck a piece of solid brass rod, larger than the hole in the nut, in the lathe and turn one end down until it will slip into the hole. While the piece is in the lathe, drill a hole, for the gas entry, in the end deep enough to reach into the uncut section. Cut off the piece and drill one (if no gas feed to the magazine) or two 3/32 inch holes in the side or bottom. Insert the piece(s) of 3/32 brass tube into the hole(s), this assembly into the nut, and solder the mess together (see Figure 3). You are less likely to get solder in the threads of the nut if the nut is on the top during soldering. I use a brick as my fireproof surface. Make sure that there is enough of the machined end inside the nut to act as a bottoming surface for the piston. Instead of brass tubes you could drill and tap one or two holes for a hose nipple.

    A non-lathe method is to again use solid rod but drill out the hole in the nut for the rod. Drill a hole in the rod end for the gas entry and the hole(s) for the feed tubes. You have to be careful in soldering the pieces together as there is no handy shelf to keep the nut from falling down on the rod.

    If during the tweaking of the piston you find that the rod sticks too far into the nut you can grind it down. Bore out a scrap "T" or union. Cut off the bored end so only the threaded portion remains. Screw this into the nut and after clamping it in the vise, use the Dremel bit to remove some of the rod. The cut fitting end will protect the threads on the nut.

    The next piece to be made is the barrel (see Figure 4). I use a double thick brass tube bought from Campbell Tools Co., 2100 Selma Rd., Springfield, OH 45505, (513) 322-8562. Their part name is Brass Tubing Half Hard very sturdy - 1/4", and comes in 1' lengths. This will make 3 4" barrels. This gives better ding resistance under fire than the brass tubing in the hobby shops. Otherwise solder two sizes of regular tubing together for strength. Figure 4 illustrates the following steps. Take two of the compression rings from the fittings you bought and solder them on one end of the tubing. Chuck the assembly in the drill press or lathe and file/turn the outside of the rings down so that the barrel will slide smoothly, but not loosely, into the restrictor. Cut the assembly at the edge of the slope/flat joint the end ring to leave a flat surface for the o-ring. Be sure that this cut is square or the o-ring will not be properly compressed. Note that the Dremel bit is slightly smaller than 5/16 so that barrels and pistons made for fittings bored with a 5/16 end mill will not fit!

    The last piece needed (other than various tubing for magazines and feeds) is the magazine fill fitting (see Figure 5). I use a sweat-on air conditioning fill valve. It resembles a tire valve. Remove the valve core and drill out the center to 3/16 inch. Drill through the side below the threads with a 3/32 inch bit for the magazine gas feed, if used. Insert a 3/32 brass tube into the hole and solder the assembly to the magazine, and also solder the tube to the fitting. Run the 3/16 bit down into the assembly again to clean it out.

    The last tip for this article is that you might want to drill the magazine feed portion of the "T" out to the next larger drill size (13/64"). This insures that the BB will not hang up at the joint between the magazine and the "T" fitting, should the parts be a little misaligned.

    A drawing of an "assembled" gun.

Return to Construction Articles