SpudFiles

so Im making an aluminum coax and i don't want to buy marine epoxy like everybody uses, what are your thoughts on elmer's fiberglass resin?

For piston casting it should be adequate, have a look here for advice on built up construction in order to save weight and material.

i have made pistons out of pieces of cutting boards fine, its the endcaps i need to epoxy

Ah, in that case what's the diameter of your chamber and what pressures are you planning on running at?

inner diameter is .745 and barrel is .437. i have a custom products regulator and a couple different hpa paintball tanks so from 0-300 but i can go higher. i was thinking about seeing if someone could make some aluminum bushing on a lathe and then i would just braze it all together and not worry about it. got a nice qb-78 rifle stock to go with it

I can't speak for polyester resins as I've never used them for spudgun applications, however a quick google search turned upthis topic on a boat building forum that isn't very encouraging...

What's your objection to some "proper" epoxy like this?

It's not exactly expensive and besides, with some care when mixing it will last you several projects.

eh thats like as much as the tubes cost. recently for my experimental coax's ive just been using some $1 epoxy from the local harbor frieght. its handled 300psi but its actually pretty thick, it doesn't form into holes that i drill into the sides of my tubes. maby i could thin it up a bit.

Uhmm I tried polyester resin before, I won't recommend it, it shrinks too much to be useful... besides it is quite brittle so I won't use it where there is significant forces involved...

heat up the thick epoxy you can get it to run like water, but it hardens quicker so be quick, i have hot plate and just put some scrap sheet metal on top and mix epoxy on its lowest heat setting then just before i need it put the temp to about 1/2 power and suck it up with a syring and use it.

From what I understand polyester resin is a little lower in impact/compressive strength than most epoxy and typically less adhesive strength, however that is why you add fiberglass to it. Hence 'fiberglass resin'.
With somthing as geometrically simple as a cylinder you won't have much trouble getting it to form. When properly mixed with chopped-strand fiberglass you'll have a tough time fragmenting your piston with small caliber firearms. No joke.

alright probably try heating it and test it on a .177 coax today. Once again, i am not making the piston, its the end caps. ive been using this http://www.harborfreight.com/super-stro ... 92665.html

Ah, that's similar to araldite. I would suggest the method of construction used here, tape wrap and generous slopping of epoxy.

yeah thats what i have been doing, but i always have a really hard time with the pilot. this time i think i will try to epoxy the pilot first. thats always the hardest part for me. the outer tube is 17 inches and the barrel only 13. hopefully i can just drop the piston in, and center the barrel from the muzzle side.

Have you seen this advice for barrel centering? I usually put piston and pilot last.

Yeah I usually have a hard time with the pilot so I'm gana do it first and center the barrel from the muzzle side this time. Ima try and look for electrical tape that isnt so wide today.