SpudFiles

I am making a coaxial bb gun with 1/2" copper, 3 feet long, and a 1/4" brakeline barrel. I would like to make an epoxy plug in the middle of the three foot length to seal off one end, and use the other end as a silencer. I will be using marine 2 part low viscosity epoxy (the stuff JSR recommended in of his tutorials) and I am having trouble figuring out how to get the epoxy in there to cast it.

Should I just dump it down one end of the pipe (the silencer side to not screw with the piston's sealing area) or should I drill a hole in the side of the pipe where I want to cast and pour from there? I am also wondering how I should seal the cardboard I will use to hold the epoxy in place. everything will be about 1.5 feet down 1/2" pipe, so it makes it difficult. Thanks for any info.

Get some epoxy putty and mash it into a pipe w/ same diameter as the one you're planning to block.
Oh, lubricate the sides first

Epoxy putty is not quite right for what I am doing I don't think. The marine epoxy is extremely strong, and from what I have seen on this site is that it doesn't really cut it (I will be using this 300-400 psi, if possible with a shock pump). Also I already have the marine stuff. Thanks for the quick reply!

How smooth do you want your chamber/silencer? You could cut your chamber/silencer where you want the plug and then either add a coupling too reattach the two pieces or use epoxy to attach them.

I want the gun to be as smooth as possible, aesthetics are a big part of this project, so a coupling is out. The second idea sounds better, I could cut it in half, cast the plug, and then cut a small amount of pipe away from the plug, leaving what would hopefully be a small rod/spigot of epoxy to slide and epoxy the silencer on to. The only problem with that would be the seam, but that is not a huge issue.

I am still on the lookout for other ideas however, so keep the ideas coming!

actually epoxy putty will do a good job they have one made especially for metal, i used it on my metal coax .

Is it cheap and readily available? I am a little tight with cash, and I already have the other stuff, but still, I am interested.

Should I just dump it down one end of the pipe (the silencer side to not screw with the piston's sealing area) or should I drill a hole in the side of the pipe where I want to cast and pour from there?

I've used both methods, but for the situation you describe as you said it's hard to get a plug that seals. You can either pour some PVA on your cardboard disc (assuming it's a tight fit) glue first, wait for it to set then pou the epoxy, but I prefer to use the following method as illustrated:

1) cut the chamber pipe in half around the point where you want the plug.

2) attach the barrel as you would do for a normal co-axial as described in my epoxy how-to, and allow the epoxy to set. The epoxy plug need not be too thick as it will be reinforced later.

3) resting them on a straight angled surface (I like to use a marble stairway) to ensure alignment, glue the two ends of the chamber pipe together with JB weld or similar. It doesn't have to be a sealed join, just enough to hold the pipe together. Once it's set wrap the join in duct tape or similar to prevent leaks and pour epoxy from the end of the pipe which doesn't have the barrel attached to it.

The result will be very strong and if you've done your alignment homework well, a bit of filler and sandpaper later and the join won't even be visible

Alright, I'll do that tomorrow. Should about 3/4" long plug be enough? (overkill is fine). For step #2, I assume I will just center the barrel with supports while the glue is curing, but I can't find specifically what you mean in your epoxy casting how-to. Thanks for the detailed advice!

For 1/2" copper, a 1/4" thick plug is enough, but nothing wrong with a bit of overengineering

To keep the barrel cented, cut out some 1/2" disks from thick cardboard with a hole in the middle the same size as the barrel, slide them down the said barrel on the breech side temporarily to keep the barrel centres while the epoxy cures then remove them later.

Alright great, that was what I was thinking. For surface prep, should I just clean it with paint thinner (the methyl ethyl stuff) or should I rough it up like pvc? The instructions say use the paint thinner, but you've had a lot of experience with this kind of stuff. By the way, the cartridges you've made are awesome, I hope they work out.

Unless there's oily residue on the area to be glued, I don't normally wash with solvent. Even with metal parts I usually rough them up with a file and coarse sandpaper, then give them a few quick bursts with a blowgun to remove the dust.