R/C Naval Combat

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



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.



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.



Now this last photo is the main part of the cannon, partly assembled.


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.

 

quote:

---

Originally posted by Greg McFadden

... the copper tube was also expensive.

---

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.








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



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.




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.



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)





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!



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)



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


 

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.



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



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



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.



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.

Being stickied might be nice so it doesnt get rebumped regularily.

I see some missing images though.