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Thoughts on real rifle barrels and hybrids

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: inonickname » Fri Jul 10, 2009 6:39 am

mark.f wrote:That's not the maximum pressure, it's the average pressure from ignition to equilibrium.


No, it was the average peak pressure over a number of shots. However, I suspect he used it at much lower mixes more often. As rag noted, the max 10-15k psi was closer to the max GGDT prediction.

And anyway, who cares about chamber pressure? nothing wrong with 933 meters per second.
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Unread postAuthor: Ragnarok » Fri Jul 10, 2009 7:45 am

Evidently, I need to explain what I mean by average pressure, because neither of you are quite on the money.
This is the average pressure exerted on the projectile in the barrel. Nothing to do with peak pressure, nor chamber pressure.

Basically, it's muzzle energy divided by barrel volume (being careful to use the right units).
It gives an idea of a launcher's power relative to it's size, considering "valve" flow, C:B ratio, etc.

For comparison, A 0.8:1 C:B combustion is ~30 psi. HEAL is about 150 psi, pretty respectable for a pneumatic, virtue of its valve and large chamber.
HEAL 2 (if ever finished) will be around 250+ psi, a big improvement - but somewhat short of another project which is looking lined up to manage 500+ psi.

inonickname wrote:Really? A 200x mix has a 3000 psi pre-ignition pressure

Not quite 3000. Closer to 2925 psi to be pedantic.

I will admit error on my part, because I was calculating from a 2m barrel, when it was a 1.8m barrel. Redoing the calculation, working from a 1.8m long 20mm barrel and a (predicted) muzzle energy of 15000 joules (11,000 ft-lbs)...
Average pressure on a 200x mix will therefore be no more than about 4000 psi (actual calculated figure is 3850 psi).

It may seem low, however, remember, this is a ~0.2:1 C:B ratio launcher, so actually that's a bloody respectable average pressure.
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Unread postAuthor: inonickname » Fri Jul 10, 2009 7:51 am

Oh, nooow the figures make a lot more sense- that's a lot fairer method of judging cannon energy.

Do you know the figures for peak chamber pressure for the ETG and the hybrid? By rough calculations the ETG would be roughly three times higher, with a much higher temperature.

So therefore- by your measurement, the ETG is easily the most powerful cannon here? It makes sense in a way, really.
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Unread postAuthor: Ragnarok » Fri Jul 10, 2009 8:42 am

inonickname wrote:Oh, nooow the figures make a lot more sense- that's a lot fairer method of judging cannon energy.

It's something that basically takes dependence on size out of the cannon's muzzle energy, and lets you put two cannons of different size on equal footing.

Most of the time it's not needed, but it can have its uses.

Do you know the figures for peak chamber pressure for the ETG and the hybrid?

I can only guess at both. Like I said, for the hybrid, 10,000-15,000 psi.
The ETG is probably at least that much, and likely more, but unfortunately, there's not enough information to know for sure.

So therefore- by your measurement, the ETG is easily the most powerful cannon here?

It produces the highest average barrel pressure, so by that definition, yes.
Bear in mind even in spite of its small barrel size, that it's power is up in the range of 7.62x39mm ammunition. It shot through the ballistic pendulum the first time.

Somewhat underrated I think.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 10, 2009 1:26 pm

If you're muzzle loading then problem solved, the ammunition is technically "pre-engraved" in the same way that most recoilless rifle ammunition is.
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Unread postAuthor: FragmentedSanity » Sat Jul 11, 2009 2:13 am

Id say your best bet for using a rifle barrel would be to us pure lead cast as round balls. You might be able to find shot gun pellets of the right size to save casting your own. Round balls wont get blown apart in the barrel and they have less material contacting the rifling so they wont need as much pressure.
Similar to what Jack states above, you could use a short length of the barrel which has been cut off as a die to pre cut the rifling and and ensure the ball is the right size.
I don't remember off hand but Im pretty sure it was 000 buckshot that fits nicely in a .22rimfire barrel. That would be a good place to start. A decent hybrid mix behind that should work, at least thats my theory.
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Unread postAuthor: CpTn_lAw » Sat Jul 11, 2009 9:31 am

All that talking about Larda's hybrid and ETG... :roll:
After all these years Rag, it still strikes me how you sometimes can be sarcastic lol (no offense to take ;) btw nice artworks )

To get back on topic, I'd say get yourself a barrel, and try! nothing better than experimenting when you've thought about it enough.
Having a rifle-grade barrel will most certainly be a good thing, not only for your current project. 25$ isn't all that money for a steel rifled barrel.
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Unread postAuthor: inonickname » Sat Jul 11, 2009 9:32 am

FragmentedSanity wrote: don't remember off hand but Im pretty sure it was 000 buckshot that fits nicely in a .22rimfire barrel.


I don't think so, 000 buckshot is 9.55 mm if i remember correctly.
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Unread postAuthor: Ragnarok » Sat Jul 11, 2009 12:02 pm

inonickname wrote:I don't think so, 000 buckshot is 9.55 mm if i remember correctly.

9.1mm I think, but the point stands. You want something like F birdshot, which is a mite over 5.5mm.

Also, me, sarcastic? Never.
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Unread postAuthor: cannon monkey » Sat Jul 11, 2009 1:04 pm

didnt read all being smart a** here but any ways why not make a rifed barrel then cut off a few inchs and make that a mold so the amo already has the riffed marks wont slow down to much and will give nice spin on it?
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Unread postAuthor: MrCrowley » Sat Jul 11, 2009 5:32 pm

cannon monkey wrote:didnt read all being smart a** here but any ways why not make a rifed barrel then cut off a few inchs and make that a mold so the amo already has the riffed marks wont slow down to much and will give nice spin on it?

I was thinking about that but I was wondering if the force would be to great for the projectile and it would simply jam, loose it's "rifle track" or break apart. Because if you pre-rifle the bullet, the bullet will have to follow the rifling path in the barrel and it initially might be too powerful and make the bullet go out of line or something.
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Unread postAuthor: ramses » Sat Jul 11, 2009 5:44 pm

MrCrowley wrote:
cannon monkey wrote:didnt read all being smart a** here but any ways why not make a rifed barrel then cut off a few inchs and make that a mold so the amo already has the riffed marks wont slow down to much and will give nice spin on it?

I was thinking about that but I was wondering if the force would be to great for the projectile and it would simply jam, loose it's "rifle track" or break apart. Because if you pre-rifle the bullet, the bullet will have to follow the rifling path in the barrel and it initially might be too powerful and make the bullet go out of line or something.


I disagree. If the projectile can handle blackpowder in a muzzle loading firearm, it should have no problems in a hybrid. that said, ball ammo is loaded with a "patch" which grips the rifling.
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Unread postAuthor: MrCrowley » Sat Jul 11, 2009 6:34 pm

Ok good to know. Like I said I don't really know much when it comes to this so i'm just hypothesizing on most things :)
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Unread postAuthor: jonnyboy » Sat Jul 11, 2009 7:54 pm

ball ammo is loaded with a "patch" which grips the rifling.


I have to disagree on this one. :? Even though my knowledge of firearms is almost non existent I do know that ball ammo in a rifled barrel = smooth bore barrel :D . Also just like in airsoft because its a sphere its going to be affected by spin just like an airsoft bb with hop up. So I know the ammo is made smaller than the barrel so could the patch be to make sure it doesn't damage the rifling?
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Unread postAuthor: mark.f » Sat Jul 11, 2009 7:58 pm

Well, I don't know about that, but a rifled ball ammo sounds a bit useless, although they have been used before...

Image

The easiest muzzle-loaded rifled round I can think of is the Minié ball, essentially a pellet in that it has a skirt which expands into the rifling, but smaller than the lands so it can be muzzle-loaded easily.
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