Anatomy of a fast gun cannon

Discussion in 'Weapons & Pneumatics' started by GregMcFadden, Nov 3, 2008.

  1. GregMcFadden

    GregMcFadden Facilitator RCWC Staff

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    Let me preface this by stating that there are many many ways to do the breech. This is one. If you have never seen one in person, BUY ONE FIRST or be prepared to learn on your first one and fix it.

    I have made many, many cannons over the years. And to be frank, if your time is worth anything at all, and you want this kind of cannon... order them from BC or others who make them.

    these cannons are dynamic devices, where the two adjustments that are available interact with the co2 pressure, piston mass, and spring stiffness to function. If any is too far off, the cannon will not function properly. Too stiff a spring and you may see multiple shots per cco2 burst. Get everything completely wrong, and you can full auto (both controlled and uncontrolled). It takes trial and error.

    First off, you will need tools and materials:
    Solder
    flux
    teflon tape
    1/4" thick wall tubing. Found in home depot commonly
    3/32" OD brass tubing. hobby shops, mcmaster.com or smallparts.com
    1/4" T fitting
    1/4" RT Angle fitting
    Caps
    Appropriate sized O-rings (depends on breech design) one for the breech, one for the fill port cap.
    Solid Rivet (see www.mcmaster.com) Rivet shown is a BC rivet
    Spring (see www.mcmaster.com or www.smallparts.com) the spring shown is a BC spring


    the brass fittings are either flare fittings or compression fittings, depending on what you have available. The T is always a compression fitting.

    and two of the handy ones: a RCBS deburring tool and a small tube tubing cutter

    [​IMG]

    Take a look at the base of the cannon. The spring should be chosen to fit over the piston and the T fitting sometimes has to be bored out appropriately. It all depends on what is available.

    [​IMG]

    This is one method of creating the breech. All that needs to be done is provide a way to compress the o-ring in an adjustable manner. the o-ring should be sized so the bb will just drop through it when it is not compressed. Again, what you make depends on what is available to you.

    [​IMG]

    Now this last photo is the main part of the cannon, partly assembled.
    [​IMG]

    the cap at the base of the T can be screwed in to adjust where the piston sits and the preload on the spring. If you are making your own for the first time, cut the spring long and then shorten as needed.


    that is a short anatomy of a fast gun cannon. that particular one is a 5 year old BC cannon. General operation is as follows. gas flows to cap at bottom of T. This pushes piston up, bb sitting on top of it. gas then flows both around the piston and down to end of magazine, pushing BB's forward till they are stopped at the piston.

    while this is happening, the bb on top of the piston moves up to the o-ring in the breech and stops. Pressure builds up and bb is forced through breech, firing out barrel.

    common issues I see:
    Over-tweaking: no bb's fire. or you can multifire as the pressure rises enough in the magazine that the pressure difference between the base of the piston and the top is not sufficient to keep piston up. piston drops and another bb moves into place. First bb fires. process repeats. this error, while cool is difficult to repeatedly produce, although I have done it accidentally.

    Fit around piston too loose: symptoms can be similar to over tweaking. larger gaps = lower pressure drop across piston = lower max transient pressure inside cannon before piston falls. Way too loose and spring can sometimes jam.

    Fit around piston too tight: Piston jams in up position, cannon does not fire repeatedly.

    Cannon fires multiple rounds and then stops: either overtweaking or the piston is too short, allowing two bb's to pass by before moving up enough. Can be a symptom of loose fit on piston.

    Poor feeding: Not having at least a 10 degree angle WRT the horizontal on last inch of magazine leading into T fitting. Kinked tubing. bad/rusted bb's. lack of cleaning cannons out after day of battling.

    BB jams in barrel: barrel dirty or dented. bought wrong size of barrel. some barrels will only work with some brands of BB's. copperheads tend to be a skosh smaller, daisy competition have always been a bit bigger when I bought them. Mcmaster thick wall tubing tends to be a bit smaller on the ID than the tube from smallparts.

    BB's: check and sort BB's. I have seen everything from nicely round BB's to bb's that only approach round when viewed from more than 10 feet away.

    I hope this helps, please add other advice if it is available.
     
    John Boddy likes this.
  2. rarena

    rarena Well-Known Member

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    This must be a good place to start my fast gun build I promised. I'll be starting on that this week. Stay tuned and thanks Greg for reminding me I wanted to do it. Nice photos and overview.
     
  3. GregMcFadden

    GregMcFadden Facilitator RCWC Staff

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    I think it is also fair to note that I ballpark priced out the components at home depot last weekend and came to ~25-30$. For that price is is definately worth purchasing them premade unless you can find a place with the brass fittings for a lower cost. Here the T's are 5$ each, rougly same price for the right angles and caps are almost 2$ each. the copper tube was also expensive.
     
  4. djranier

    djranier Well-Known Member

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    Yes Rick is trying to keep everything as low cost as possible at BC. He is not running Charlie's business trying to make a profit off you guys, but for the enjoyment he himself gets out of the hobby. Thats why Don C and myself also help him as much as possible, BC is trying to keep the prices as low as possible, for when a new person (recruit) wants to get into the hobby, its semi affordable to get that first boat.

    As Greg says go price the parts, and you will find with the premade BC tested guns, that you can't beat the price.

    I look forward to when Greg starts selling his, I saw that video, and I'm ready to get some myself.
     
  5. GregMcFadden

    GregMcFadden Facilitator RCWC Staff

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    video? was that one of justin's? Biggest problem I am having right now is lack of manufacturing capacity... I am making some as my time permits for folks... justin has his set of 4, 4 sets are ready for Craig, and there are now 2 sets down in austrailia with another two on the way.

    I guess that means I should get that tripple built up and tested...
     
  6. djranier

    djranier Well-Known Member

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    Yep the one that Justin posted back a couple of months ago.
     
  7. BoomerBoy17

    BoomerBoy17 Active Member

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    Im most likely going to order BC guns for my ship. Im glad he does that for the recruits(being one) and im happy with the prices. Yea, tripples would be nice. I definitly see why u used duals first, its only logical.
     
  8. GregMcFadden

    GregMcFadden Facilitator RCWC Staff

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    Actually, I did duals first since I wanted to arm my tirpitz (well it is justin's tirpitz now)
     
  9. JohnmCA72

    JohnmCA72 Member

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    & here we thought it was the meth-heads who were stealing all the copper tubing... [;)]

    JM
     
  10. GregMcFadden

    GregMcFadden Facilitator RCWC Staff

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    yep... you best be hiding your refrigerators from me or I might break in in the middle of the night and make cannons ;)
     
  11. rarena

    rarena Well-Known Member

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    Alright, the start of the fast gun build. Parts maybe be listed wrong as I find the companies change things from time to time. I will try to list what I can.


    [​IMG]


    [​IMG]


    This is all the parts as they are assembled to make a gun

    now starting with the gun barrels....

    IRCWCC allows 5 inches from breach so make them 5 inches
    Cut a 3/8 sleeve to go over them,
    barrel is made of 1/4 round tube brass,
    sleeve is 5/16 round tube brass

    Smallparts.com - TTRB-04H-12 and TTRB-05H-12

    [​IMG]

    The sleeve is soldered on the the barrel using silver solder (for strength). The end is squared with a file. Then the other end is cleaned where the sleeve meets the barrel. The nut you see here is the breech nut. You will get a few of these from the fittings you buy. The nut slides down the barrel, makes contact with the sleeve and tightens a o ring against the 90' fitting making a pinch point for the bb to squeeze through. Drill the exit end of the barrels for a safety pin.


    [​IMG]

    Now to work on the 90' fitting to make the breech
    lowes 1/4 copper tube
    lowes A-14 all tube elbow with inserts (compression)
    lowes A-1 1/4 delrin sleeves
    Smallparts.com o ring ORB008

    It is very important to orient the 90 the correct way. If you look into it, you will see it is drilled one way then the other. you want the barrel end to be the dominate bored path. The bb's must come up and out without getting stuck. Then we make a place for the barrel to sit in. My barrels slide in. There are other ways to do this and I believe BC's are flat surface to flat surface. They both work. The difference is fittings and o rings. To bore the 90 so the barrel slides in, I use a 5/16 dremel bit called a forstner bit. Here is the pict.

    [​IMG]

    I open it up a little with a drill and then run the bit down all the way even with the threads (and the bit)

    [​IMG]

    [​IMG]

    This leaves you with a nice barrel hole. It is important to get it straight or your barrel will stick out at a angle. Don't ask me how I know that either!

    [​IMG]

    Then cut a length of copper tube(3 inches) and solder it to the other end of the 90' this can be trimmed to height later. Ream the copper tube and the 90 out with a reamer (drill bit if you have to use it) and make sure the bb's flow freely
    Delrin sleeve and nut finish out the breech elbow

    Ok, on to the interrupter...

    Lowes A-10 1/4 all tube union w/insert compression
    smallparts.com beryllium spring CS-53
    stainless steel tinner's rivet (I've seen SS nails used also)

    [​IMG]

    Take the piston(rivet or nail)and smooth out the top sharp edges. You want this to go up and down and not catch. Ream the union both ways, Smooth is good! Cut a chunk of spring (about the rivet) and set in union. Ideally you want the spring to hold the rivet out of the middle(you can just see the top of the piston) without impeding bb's
    if it sticks up too much the spring is too short and will malfunction. I go long and trim it down so that it is relaxed right out of the bore. Hard to explain in words, may need more photos.
    Put spring on piston, put in hole and bounce up and down. Any catching must be eliminated. Now on to the cap. I'll pick this up later, one photo of cap parts

    [​IMG]
     
  12. rarena

    rarena Well-Known Member

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    Without holding a gun, having a ship battled for some time or basic metalworking skills, some might not. I bet your dad reading that might almost put a gun together in no time. It's not for everyone but if there are any questions, I plan to add to this to make it more reader friendly so go ahead and help me tweak it. Boomer, I will try to get you up the next time we make guns, last time I made 9-10 complete ones and a few spare barrels (25) for Don E. This build will also tell where to find parts, which held me up for quite a time.
     
  13. rarena

    rarena Well-Known Member

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    ok interupter time.
    smallparts.com TTRB-02-12 3/32nd tubing
    smallparts.com ZRB-04 1/4 brass rod

    Drill a hole across the 1/4 brass rod for the 3/32nd tube near the end. Cut the 1/4 rod to about a 1/2 inch length. Solder in the small tube. Drill down the brass rod from the top, the 3/32nd makes a tee at the bottom. You want to drill until you hit the 3/32nd tube. Go through the 3/32nd tube. You want air to come from this going up. Don't go all the way through the brass rod bottom. The bottom needs to remain sealed. Solder the 1/4 rod to the hole in the cap nut. Make sure it sticks in but not too far. Chase out the 3/32 tube with a small drill to make sure it is open. It should resemble a tee but it does not have to be as long as this one appears.

    [​IMG]

    for assembly, place spring on piston, put piston in bottom of union. Use blue locktite on bottom of union. Tighten cap until piston is even with bottom of middle hole.
    CA glue the cap top threads. You are just filling in gaps here so air doesn't escape. All of this is reversible if you need to take the cap off.

    Now for the magazines...
    Lowes 1/4 copper tube
    Lowes Flare fitting 1/4 tube to 1/4 tube
    refrigerator cap (I don't know where to get these)
    Smallparts.com 3/32nd round brass tube
    Lowes delrin sleeve

    [​IMG]

    Cut the copper tube to length. I like to go with 10 inches length for a 50 round magazine.
    Cut the flare fitting. You want threads and nut, cut the threads on other side off. Drill a hole for 3/32nd tube. Slide copper tube in. cut 3/8 length of 3/32nd tube, slide in drilled hole. Solder all. Ream out the copper with a 177" reamer

    [​IMG]

    Now drill the small tube and make sure you go through into the copper tube. You want air to go into the magazine here to feed bb's.

    [​IMG]

    Roll bb through tube, fix/ream if needed.
    Add nut and delrin sleeve on union end and attach to union middle.

    Assemble gun and fine tune. CA glue all tubing to brass before sliding it on, I use windex spray bottle straw over the 3/32 fittings hose, zip ties over the 1/4 tube to hold it. Place in a bucket of water and make sure you have no leaks from fittings. Fitting may have to be reamed out more after assembly, especially if you had to tighten some a lot. Good luck and ask if you have any questions.
     
  14. Kun2112

    Kun2112 Active Member

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    Does anyone have a source/part number for the piston/rivet?
     
  15. DATDAVFred

    DATDAVFred Member

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    From BC. Probably best source
     
  16. Tugboat

    Tugboat Facilitator RCWC Staff Admiral (Supporter)

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    BC does not sell the interrupter pins nor springs separately from their cannons (i.e. they're in a cannon but no extras come with nor can be bought). So you need to hunt down a source.
     
  17. NickMyers

    NickMyers Admin RCWC Staff

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    Strike sells injection molded pins individually if you really can't find something to modify at your local hardware store.
     
  18. DATDAVFred

    DATDAVFred Member

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    ok, so that means i better keep my guns clean . and make sure i dont loose the spring or allow corrosion. thanks for the heads up. also i need to be sure before i speak. lol
     
  19. Time Lapse

    Time Lapse Member

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    I am looking on youtube for a video on how to make cannons like yours or any RC Cannons, I can't find any .Do you know of any on youtube?
     
    Last edited by a moderator: Apr 6, 2015
  20. NickMyers

    NickMyers Admin RCWC Staff

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    There are none public that I am aware of. Really recommend purchasing your first rather than trying a DIY without an example in hand.
     
    Last edited: Feb 14, 2017