4 inch piston

[SP00K]

What should I use for my 4" diameter piston?

Right now, I was thinking a 3" endcap with a mousepad for a sealing face, but I did just read a thread about epoxy casting one (although I have no experience there). Would 4 inches be viable for an epoxy piston, or is that too big?

[clemsonguy1125]

Well that take a lot of epoxy unless you cast it around a pringles can or something, then filled the can with great stuff or something.

[Lockednloaded]

A 4" cast epoxy piston would destroy valve bodies; even if filled with foam you would need a substantial amount of epoxy and a sizable bumper. If I were you I'd use the 3" cap. The only issue with that though is that pressure rated caps are curved, but if you find a DWV cap, it should be flat

[clemsonguy1125]

That would be heavy and crack or shatter easily, you would need a large heavy duty bumper for that.

[Lockednloaded]

he'll need a bumper for any piston this size, DWV is just as shatter prone as regular PVC so shattering should not be an issue with a bumper. Epoxy would be much heavier, and because it is so durable, it would not shatter itself, but instead the fittings which would be way more expensive than replacing a piston

[jonnyboy]

Yah a dwv cap would work well as for the bumper you could use half a nerf football or possibly a tennis ball.

[clemsonguy1125]

I didnt mean it would shatter because it was DWV just that PVC shatters easily, Tech had a lot of issues with this on his Mouse Musket if I remember correctly, he will need a bumper with any piston, a PVC piston will just require a heavier duty piston.

[SpudBlaster15]

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[Technician1002]

The difficulty with the Mouse Musket was dealing with the hollow endcap. That does not provide a large flat surface for a decent bumper. My Dragon suffered the same problem. It too used an endcap. It used a 3 inch endcap (pressure rated domed) against a o ringed seat like the Mouse Musket. That cannon has a 6 inch PVC chamber, a 3 inch piston cylinder, with a 2.75 inch seat into a 2.5 inch PVC barrel. Getting a bumper that did not become chopped liver for dinner after a shot proved to be a problem. The edge chopped any bumper, which shattered the piston.

The QDV and the replacement piston for the Mouse Musket were both used to get away from hollow back pistons. They were too much trouble. A flat back works much better.

The piston in the ABS Cellular Core Cannon uses a flat PVC washer between the piston and bumper to take care of that problem. I am surprised the washer has not broken yet.

Cellular Core Cannon piston uses a washer to keep the bumper out of the piston recess. I think the only reason it has lasted so long is the low pressure it was used with most of the time.


The washer was made with a hole saw. PVC pipe was heated and pressed flat first.

[spudtyrrant]

uhmw FTW, i have some extra 4" round stock that i could send you if you like, you would have to pay shipping of course.

[Crna Legija]

the bore of a 351 is 4'' so its piston would fit

[jackssmirkingrevenge]

A 4" cast epoxy piston would destroy valve bodies; even if filled with foam you would need a substantial amount of epoxy and a sizable bumper.

With a bit of thought it can be made light and strong without using too much material. Some useful advice here.

[SP00K]

Thanks Tyrrant, but the parts for this cannon cleaned me out for a while .

So if I sliced off the round top to my 3" endcap and put some flat pvc over both ends, could that suffice? I'm looking at 3 old mousepads I have, thinking 2 for the bottom as a bumper and 1 for a sealing face.

Right about now my gun is entirely finished except for the piston. Barrels are straight and edges are smooth and true. I'm using a sprinkler as my pilot valve.

[Technician1002]

I melted some ABS over the weekend. It may be possible to cast the stuff. That could be a fantastic piston. More testing is needed.

[clemsonguy1125]

Whats the tempature needed to liquify ABS, how long does it stay liquid, I can see it being used for pistons, vortex blocks, ammo, and asthetics.