Is this a good Coax design?

[linuxexorcist]

I've been reading on the site for a while, and while I've built some basic cannons, nothing special has been wrought by these hands, I have built a basic Over-under ball valve pneumatic, a metered butane 1" bore combustion, and a more advanced metered butane golfball gun:
http://s771.photobucket.com/albums/xx35 ... C_8948.jpg

now I am planning something a little more special, I want to build a copper piston musket (I mean, can't use "rifle") and want a little input, primarily on epoxy (JSR?)



The image should hopefully speak for itself, a few notes and questions:
1. the thing with "Schraeder" and "1/4" NPT nipple" pointing to it is an endcap and coupler with a little pipe between them, filled with epoxy, drilled and tapped.
2. I hope to solder the coupler to the end of the pipe, will the joint hold up to the piston's force?
3. in soldering it, will it melt or otherwise damage the epoxy?
4. would it be easier to find some 5/8" rod and drill and tap that and use a coupler between the barrel and rod?
5.What pressure would i need to achieve to get a speed near 120m/s (just under Canadian classification of a firearm)?
6.the magnets is to hold the ball bearings in place before firing, they can easily act on a >1g object at 1/4" away

I am looking to build a stock, based on this:
http://www.spudfiles.com/forums/draguno ... 21623.html
and attach a rail and scope, hoping i can get accuracy to justify it

If my handwriting is illegible, or if you have any other questions, let me know.

[Technician1002]

Soldering temperatures damage epoxy. The muzzle end can be assembled using a reducer filed out so the barrel can pass through it.

The breech can be done with a female threaded adapter on the end of the chamber to permit servicing the piston. It would look something like this one at the muzzle.

Near the breech of the barrel you will want some kind of support to keep the barrel centered. The small magnet could be placed in the chamber but it is not needed. If the piston moves back no more than 1/2 the barrel diameter, the piston will prevent the ammo from falling out the breech. Without a magnet, cheap ammo such as marshmallows, fishing weights, golf t's, and marbles can be used.

Edit, I noticed your sizes.. maybe airsoft, pellet gun pellets, rabbit food, etc.

[linuxexorcist]

I would like the compactness of the drilled and tapped method, I'll look into using a 5/8" (1/2" nominal OD) piece of brass rod drilled and tapped, so no epoxy parts to hurt, and just a wood piston.

Edit:
would aluminum or other cheaper than brass materials work? can i solder that?

[Technician1002]

Stay with copper. It solders best. They make a special solder for aluminum, but it is really hard to do right. Aluminum oxidizes rapidly causing difficulties with soldering. Cleaned and fluxed copper solders very well.

[linuxexorcist]

i can always use threaded fittings, but I'll look into copper or brass rod first
By the way, the scope I'm using is 3-9x40