OR more precisely, the geek-breech, ball-bearing interrupter cannon... [this design is based on/derived from work by Bob Sloan, the teachings of Bob H, and quite a bit of trial and error. Thanks to The 2 Bobs!] The HTML version of the CPOE cruiser class and follow-ons will be a little broken up (pump- and gun-building classes will be separate from boat-building classes, but will be linked to as seems appropriate). With that in mind, Model Warship University presents the first Offense class ZO! Schtudentz! Hyu vish for POWER, ja?! Ser goot! Ve must be able to zhoot ze enemies, ja? Vissout gunz, ve are nossing more zan convoy zhipz! Und zo, to class... You will need the following tools: Blowtorch, solder, and flux paste. Drill or drill press with bits. Tubing cutter and bender. 1/2" countersink bit (used for deburring the ends of the copper tube after cutting) You will also need the following parts/materials for EACH gun that you want to make: 1/4" copper tubing (1 foot), the following brass pieces for 1/4" OD tubing: 1 Ander-Lign Compression Tee (part # A-12), 1 Ander-Lign Compression Union (Part # A-10), 2 Compression Caps (Part # A-5). Part numbers are from the packages I bought at Lowe's, they are color-coded with a pink bar on the top of the package. Also 2 delrin sleeves for 1/4" OD tubing. Additionally, you will need a package of Panther Products large silicon fuel tubing (like for RC planes), some 7/32" stainless steel ball bearings, some Clippard 1/16" hose, some 5/32" aluminum or brass tubing and one Clippard 1/8" hose barb (thread type unimportant, it gets soldered). First, cut the 1/4" copper tubing into three lengths: a 9" piece for the 50-round magazine, a 2.25" for the uptube, and a 1/4" long piece that'll be part of the breech. You do this with the tubing bender; don't try to tighten it too much between rotations! just a little, give it a turn, tighten a bit more, give it a turn, repeat until the tubing breaks at the cut line. Use the countersink tool to clean out the ends of the tubing where you cut it; this will help encourage BBs to pass freely thru the ends of the tubes. (That's important!) Lay out the parts and it should look like below. Note that the 2.25" piece of tubing has been bent in a nice curve. It's not quite a 90 degree turn, more like 60 degrees. You must use a tubing bender to get a nice kink-free bend! I use a cheap 'spring'-type bender, there are several different types that can do the job. The two compression fittings with holes in them came from the Tee (you get 3 with it, and 2 with the coupler). These compression fittings originally come with a brass compression sleeve in them. You will need to remove that, using pliers and some ingenuity. We will be using delrin sleeves in place of the original brass ones, which leak gas when the guns are fired. The delrin won't leak nearly as badly, so we get more power [Thanks to Bob of Port Polar Bear for the education on this!] Now, we drill out what will be the bottom of the Tee. Put your 1/4" drill bit in your drill press, and hold your Tee upright with a vise (best), vise-grips (less good), or a pair of pliers (least good). I have used all three with good results. Just pay attention to what you're doing! I marked my drill bit with tap 9/16" up from the tip, so that I don't rill too far. Go too far, and you just slagged a $6 Tee, at least for our purposes. 9/16" is it. You can go a little less, but not too far. NOTE: Do NOT use a 'pilot-tip' drill bit. it will create a funky-shaped hole that will grab the ball bearing, jamming the gun after one shot. Use a plain-ole drill bit like in the picture. I killed two tees before figuring out that little factoid... Below, an obviously-staged photograph showing the bit 9/16" into the Tee. In case you're wondering, the vise has been removed from these two pics, for clarity's sake. Next, we are going to make the bottom end of the breech, where the CO2 will enter the gun... Clamp one of the compression caps into a vise (or something to hold it steady for drilling and soldering), so you can drill down into the inside of the top. We do this because 1) it lets us clamp the cap by the solid 'crown', where it's strong and inflexible, and 2) we can use the little dimple in the inside of the crown to center and guide the drill bit. Pick a drill bit that is just bigger than the threaded base of the Clippard 1/8" nipple. I'll post the size tomorrow when I can check it in the shop. Below, the hole has been drilled, and the nipple inserted. You can't see it very well, but there is a bit of solder flux paste around and under the nipple. Rar! Kree-gah! Fire! Heat both pieces evenly, and solder them together! Try to keep the nipple straight up and down When it's good, let it cool while we play with the other parts... After the gas fitting cools, grab the 9" magazine tube and the compression coupling. We will be soldering those together, too! I clamp the tubing in the vise, and sit the coupling on top, then solder. It's pretty straightforward, but if you run into problems, email me. We need to provide a means for gas to enter the rear of the magazine, as this promotes good ammo feed to the breech of the gun. We do this by drilling a 5/32" hole into the coupler that we just soldered onto the magazine tube, as seen below. More on this later! Below are the parts laid out more or less as they relate to one another... Take the Tee, and insert the ball bearing into the bottom (where we drilled the Tee out), followed by the 1/4" length of copper tubing, and then thread the gass fitting that we made onto the bottom of the Tee. Screw it on as tight as it'll go. Flip it upside down and look into the hole where the magazine tube will go, you should see a fair bit of the hole (20-30%) obstructed by the ball bearing. The bearing should freely move back and forth if you invert and revert the Tee several times. This is the time to check for jams Below is a pic of the first step, completed. Next, take your remaining tubing, and slide a compression fitting (the ones with holes, obviously) and then a delrin sleeve over the end of each piece that'll go into the Tee. You can see what it looks like at this point, below: Next, thread the compression fittings onto the Tee, and tighten them both hand-tight, then use a wrench, and tighten them more. I don't have a torque spec for these, just get them tight enough that rotating the tube is difficult but not impossible. That's it for part 1 of Offense-101, part 2 is tomorrow! In part 2, we will connect the barrel and silicon tubing to the rest of the gun, and run 1/16" tubing from the breech to the back of the magazine, followed up by function testing! All schtudenten vill be in zer seatz promptly vhen zee klass schtarts! Heil Fluegel!!! *I am especially interested in feedback from people who have 1) Never made a gun in their life, or 2) Have made lots of guns, for themselves and others. Does a part of the lesson seem hard to follow, or need more pictures? Constructive feedback is greatly appreciated.