Cup Shape Piston

[jrrdw]

The basic idea came about in talks with Rabidduck about a 4" chamber coax cannon he's building. Because of the need/want to keep pilot chamber small and possible piston tilting with large diameter pistons, I thought the majority of the piston could be in the chamber.

This way the piston can be plenty long enough to avoid tilting and still have a small pilot chamber. The part of the piston in the chamber will be hollowed out to allow plenty of flow and keep weight down. With enough surface area to do the job.

I'm sure there is plenty of things this piston can be made from.

Anybody think of this before? I haven't seen anything like it myself, but that don't mean it's not out there all ready...

[jrrdw]

Updated so it's easier to understand....

[c11man]

a better way is to take a flat cap and face it so the socket side is pointing towards the muzzle end, the sealing face would then have to be bolted to the inside of the cap

[RabidDuck]

in the making. making it out of fiber glass, 4 inches in diameter and 4 inches long. Just poured it so by monday i will put a picture of it up. Then once i get my barrel i will drill the hole and so on

[jackssmirkingrevenge]

*cough*

[jrrdw]

JSR that's close but not what I had in mind.

[RabidDuck]

ok i got pictures, its hard to see in the picture but its a little under 4 inches in diameter, and a little under 4 inches in length. I'm cheap and don't want to go and buy more fiber glass but if you think it will help i will. Here they are, btw that last one of the bottom is the duct tape, i should of used clear packaging tape...

http://img263.imageshack.us/g/piston001.jpg/

edit: instead of adding more fiber glass, cant i extend it by adding a big bumper?

[jrrdw]

Have you checked the fit in your chamber with this yet? If so, how snug or loose is it?

[RabidDuck]

i don't have my chamber yet but of course i got the 4 inch mold and it slides but its heavy enough that it has a little drag too it. It will fall out if i put it in and tip it.

[jrrdw]

Sounds about right. How are you planing on making the barrel hole? Get it in the center...looking good so far.

[RabidDuck]

i will probably find the center some how and then start with a small hole and keep getting bigger. I'm not sure how i will get up to 2.5 inches though. And would that work to add a bigger bumper instead of adding more fiber glass on it?

[jrrdw]

As for length work with what you got. Do you have a drum sanding bit you can put in your drill? Use a piece of 2 1/2" pipe and trace a guide line around it so you have something to go by.

[RabidDuck]

my dad was at fleet farm this afternoon and found the same exact fiber glass resin for 5 bucks cheaper so he got that for me along with a 7 in 1 Hole saw so i will use that to cut the hole.

[jrrdw]

The only problem with using a holesaw is it's just going to cut a circle. It wont remove the fiber glass out of the center. Remember your not cutting all the way through, just 3 inchs deep.

[RabidDuck]

yep i had a little routine going. drill a small hole and pry it out and get bigger and bigger, i'm not finished yet but i'm going to sand the rest out tomorrow. The hole is 2.5 inches but its not quite centered perfectly, but that shouldn't matter since it will be on the barrel even when it slides back it just may need some duct tape on one side. well here are 2 more pics.

http://img696.imageshack.us/gal.php?g=p ... ver001.jpg