This is the start of my proto BB cannon system. After looking at several designs, I decided that they all seem to have draw backs. The simplest cannon use a pressurized magazine, and frequently all the air has to go through the magazine to fire the cannon. this is a terrible restriction. The other style commonly used seems to look like a petry dish with the barrels verticle through it. The problem is that the magazine is partially pressurized. some magazines are 4" diameter. at 100 PSI that is over 1200 pounds of force! That is a bit of an issue. This setup is being built for .177" BBs . I am designing it so that it can be built in the basement with a minimum of tools. Sure I could chuck up a piece of brass in the lathe, but how many people happen to have one in the basement? I am using K&S brass tubing, various size brass and copper washers, a little 5/32" brass rod, a 1/4" compression union or T, and a spring. (plus a nipple). The bolt is a piece of 7/16" tubing, a copper washer and a piece of 3/16" tubing. (K&S sizes are OD not ID!!) The 7/16 inch piece is cut to roughly 1/4" long. It is not terribly important, The legth will be acounted for later. This piece is just a skirt for sealing and alignment.. A copper washer that happens to be 7/16" OD was soldered on top. Be carefull to keep it centered. The washer was drilled out to 3/16". (I think it was a #8...) the 3/16" tube was run through the hole. it was then inserted into the union (Which was previously drilled to allow an angled feed tube)(in my case. you may prefer a T). Set the end of the tube so that it is flush with the cutout in the other end of the fitting when the washer and outer assembly is flush against the other side of the fitting. This sets how far the bolt will move beyond the feed port. Mark the tube on the bottom side of the 7/16" skirt. cut it a bit long. Make the bottom of the skirt and the bottom of the 3/16" rod flush and solder. File the other end down to fit. Polish up your work with a fine abrasive. (I used a 3M pad)
The outer shell is 15/32" It will just fit over the threads of the 1/4" compression fitting. I put the in the fitting so that the feed port was completely clear and held the tube alongside so that a couple threads were showing, and cut it flush with the skirt end of the bolt. This will give you some room for adjustment in length. I soldered a brass washer on it that was a hair over 7/16", carefully centering it. The hole was much too large for the 5/32" rod to fit so I crimped a bit of 3/16" tubing around the 5/32" rod.and drilled another copper washer to 3/16"This kept them fitting tight together for easy adjustment. the pin in the middle is to keep air from escaping up the middle of the bolt until the feed port is almost completely closed. I slightly rounded the edge with a file. then I eyballed the assembly so that the 3/16" tube stuck just through the copper washer and that it was just a bit longer than a BB beyond the thickness of the brass washer. This was then soldered up, and I ground the excess length odff. (The tube and rod were about 1/2" long for easy handling.) This was carefully centered in the brass washer and carefully soldered. a hole was drilled off center for the nipple. I don't have a 10-32 bottoming tap so I just stuck the nipple in the hole and soldered it. (Part of the reason it is crooked). Sorry, I am not the greatest torch solderer yet, but an iron would screw up the alignment.. A spring goes over the bolt and fed into the fitting. the outer case is then slid over it until the bolt is just shy of the feed port and soldered in.
9/27 update: I kept blowing the joint at the rear of the outer cylinder. This was solved with a ring of 1/2" OD pipe soldered on. The rim of the case to the washers just wasn't enough. The bolt is fine because the skirt really doesn't see any force. Now I need to work on an adjustable center pin. I'm thinking a nut soldered on the back shell and a brass screw with a nub of 5/32" rod soldered to it. a bit of teflon tape to keep it from wandering.
Operation:
When air is applied, the bolt has to move into the fitting the length of the 5/32" center post before air can go up the center. At this time the feed port should be closed and all of your air goes directly behind the BB for firing. This is a very efficient way to shoot them.
(09/23/03) David Peter. I reserve the right to patent this design... Anotherwords, use it for yourself, and friends. Don't try to mass produce it without paying Royalties. |
