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new to combustibles

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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new to combustibles

Unread postAuthor: Major Collins » Mon Apr 11, 2011 9:23 am

i want to make a combustible a certain way with ideas in mind but a little indecisive , i made the old fashion combustible a couple years back
bbq lighter , pvc body screw on end cap etc

some of the things im curious about are
how small can a combustible chamber be to launch a 10 mm 10 gram lead slug about roughly about 700 fps

and what other types of igniter are there? besides a taser i know that
method

by the way how long can gas or propellent be stored in a chamber before being fired?
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 11, 2011 9:39 am

The wiki will answer a lot of your questions.

how small can a combustible chamber be to launch a 10 mm 10 gram lead slug about roughly about 700 fps


A combustible chamber will only last for one shot ;) for a non-hybrid combustion and a 10mm barrel, I don't think launching a 10 gram slug at 700 fps is realistic. If that's the performance you're after, you either have to go hybrid or consider making a big bore (50mm plus) calibre combustion and launch with a sabot.

by the way how long can gas or propellent be stored in a chamber before being fired?


The longer propellant is stored in the chamber, the longer it has time to form a homogenous mix with air so the better your shot will be :) this assumes that there are no openings in the chamber and your projectile is a good fit in the barrel.
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Unread postAuthor: Crna Legija » Mon Apr 11, 2011 9:43 am

download HGDT and play around with it till you get what your looking for.
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Unread postAuthor: Major Collins » Mon Apr 11, 2011 9:55 am

i want it to be rifle like so rather compact

would it be possible to make a combustible with decent power, rifle sized?
and i mean like a sniper size comparison lol no aint tank rifle for me

if i were to make a hybrid do i have to have extra parts to do other stuff on the cannon or can i make hybrid fuel to put into the cannon ?

what type of fps can i get out of a small projectile?

its good to hear that it propellent can be stored for a while
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 11, 2011 10:29 am

A hybrid needs a way of retaining pressure (so burst disk/piston/friction seal etc.) and a way of pressurising the chamber. You need to read up a bit more about them before you attempt one.

Non-hybrid combustions will only generate around 100 psi, so for "rifle sized" calibres, you're not going to get much power.

With my 5.5mm calibre hybrid here's some data for 16 grain 0.22" pellets showing mix - velocity - muzzle energy:

8x - 840 fps - 25.1 ft/lbs

9x - 879 fps - 27.4 ft/lbs

10x - 925 fps - 30.4 ft/lbs

12x - 983 fps - 34.3 ft/lbs

14x - 991 fps - 34.8 ft/lbs

At 1x (normal combustion) pressures, I doubt you would get something more powerful than an airsoft rifle.
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Unread postAuthor: DYI » Mon Apr 11, 2011 10:34 am

i [sic] want it to be rifle like so rather compact ["." ?]

would it be possible to make a combustible [sic] with decent power, rifle sized?
and [sic] i [sic] mean like a sniper [sic] size comparison lol [sic] no aint [sic] tank rifle for me ["."?]



Depends on how you define "decent power" (which I'll assume to mean "decent muzzle energy"). An atmospheric pressure pre-ignition air/propane gun has about 0.1% the energy density per unit chamber volume that a firearm does, so it certainly won't be decent compared to a firearm. HGDT will give you a reasonable estimate of the performance, for low speeds of course. It's up to you to simulate your design and determine what constitutes "decent".


if [sic] i [sic] were to make a hybrid do i [sic] have to have extra parts to do other stuff on the cannon or can i [sic] make hybrid fuel to put into the cannon ?


Your question is incoherent, rambling, and betrays your complete lack of research into the topic before posting this utterly pointless thread. To answer what appears to be your question, yes, you can create "hybrid fuel to put into the cannon". I recommend nitroglycerin.


what [sic] type of fps [sic] can i [sic] get out of a small projectile?


There are two possible interpretations of this query. While it is possible to exceed 10000 ft/s with combustion guns using gaseous fuels, I highly doubt your capability to exceed 300.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 11, 2011 10:40 am

DYI wrote:Your question is incoherent, rambling, and betrays your complete lack of research into the topic before posting this utterly pointless thread.


My reply was slightly more polite but the thoughts echoing through my head as I wrote it were very much the same ;)
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Unread postAuthor: qwerty » Tue Apr 12, 2011 3:18 am

Basically, Mr Collins, what they are trying to say is that you need to do a bit more research on combustion and hybrids launchers. The Spudwiki is a good place to start but remember, hybrids aren't something to mess around with and can seriously hurt you if something goes wrong. Also they can be quite tricky to make so be careful. Same goes for combustions too.
Good luck anyway.

:)

EDIT: I just realised that there is an upsidedown wolf in the spoon of DYI's avatar. :D
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 12, 2011 5:23 am

qwerty wrote:I just realised that there is an upsidedown wolf in the spoon of DYI's avatar. :D


I can't remember what the original post was but for some reason I had put Rag's then avatar into the matrix scene.
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