Of course I'm using teflon tape, I thought that's only a lubricant though, and the pipe seals when you tighten it so much that it deforms the threads. I would think doing that time after time it would eventually lose it's seal?

To seal pipe threads, especially steel, I have to put it in a vice and then use a huge pipe wrench to really apply force until it finally seals. The thing is, I'm making a piston valve gun out of steel pipe, how can I access the piston and at the same time have that joint seal completely

Very...very nice.
Question , to have the piston seal against the barrel, how did you fit the copper through the tee? Same way as if it was PVC? (dremeling out the lip)?

Yes, I'm pretty sure copper can handle hybrid pressures...the pipe is rated a lot higher than most hybrids can make.

The flux prevents the copper from oxidizing, solder doesn't stick to copper oxides. I think you also would use certain solder meant for plumbing, because it's stronger than solder ...

One more question, is iron pipe as strong as steel? I'm not talking about the malleable iron fittings, I'm just talking about the black iron nipples that I see in the hardware stores.

I'm not really worried that it would fail if its stronger than malleable... but I'm just wondering.

Haha I heard that, but I actually tried this with a 2 liter soda bottle...I used a pop in schrader valve and sealed it with epoxy. At 60 psi, the bottle rips around the valve and flies across the room. Probably some mistake I made though.

DYI: Well, you said 1/2" steel coupling...but then you said malleable iron (or same thing?)...anyway wow that makes me feel a lot safer.

nivekatoz: Are the endcaps made of malleable or black iron?

This is unrelated, but if I wanted to drill a hole for 1/4" NPT fitting, what size would I drill?

DYI, your malleable iron fittings have a burst pressure of 2200 PSI?

You know this from experience? I'll be remote firing this, but still... if iron fails like PVC, I'd rather use PVC because plastic flying into my body might not kill me.

Well before I ask that, I want to know if "black iron" is safe to use in a hybrid. Not sure what kind of iron, it just says black iron nipple.

Then the union and some of the fittings I found are made of malleable iron. Please tell me they can take way more than 150 PSI? Or am I just going to have ...

OK I know most of this now, except for the propane meter. I'm using Fuel Tool to find this out now...

When it asks for atmospheric pressure, is that talking about atmospheric pressure in our area (If we're not at sea level)?

Then it's asking for supply tank pressure... is that what you set the ...

Well since I want to fire potatoes, it's going to be 1.5" x 60" most likely (If that will still be an OK ratio). At the most I'll take it up to 6X because I will be remotely firing it from far away.

And when you put a sparkplug in there, can you just use a simple BBQ ignitor to create a spark?

How do you drill holes in steel?

Also, is it safe to use SCH80 PVC for a hybrid? I read on the archive of Spudtech forums that a lot of people are using that, but that might be old now. Is it like certain it's going to blow up after a while? Cause that would be so much easier to work with...

Alright cool. About number 3, I meant that since couplers would be there the metal would be twice as thick. Therefore drilling a screw there shouldn't affect the strength as bad as if I were to drill it directly on the chamber.
About number 4... um well I just used the wiki to try and figure it out ...

Alright... so I made a basic combustion spud gun and it works great. I realize I should have more experience with spud guns than 3 shots with 1 cannon...haha. I've built 2 pneumatic cannons before, not for spud gunning though so I think I know the basics about combustion and pneumatic cannons... yay ...