Affect of barrel on boom

[Richtee]

I have a 3/4" walled 2" cold rolled steel tube with a .25 thick baseplate welded on. It's 24" long, and I use it for mortar shells of course. GREAT launch.

 

But I am always amazed at another phenomena. I'll drop a couple gram bag of a substance not to be discussed here, and the report is sooo much better/boomier, if you will- than said substance in a tube or bag in the open air.

 

I'm no expert of shock wave prop, or whatever this would come under, but anyone here have a semi-technical explanation for this?

 

Also, I hope this is at LEAST close to being on-topic/right place. If not, would a mod please move it?

[TheSidewinder]

What you describe doing has no legitimate pyro usage, as far as I know, and certainly isn't used by re-enactors in any replica weapon that I'm aware of.

 

This sounds like a recipe for trouble, despite the interesting effect you describe.

 

But since I'm not certain of that, I'll wait until someone who DOES know for sure, chimes in.

 

And unless someone who I trust to be correct replies to this message and says it *is* used legitimately as such, within 24 hours, it's getting locked.

 

Indiscriminate use of Flash is a fool's undertaking. You're trying to find a problem to fit a solution, and not the other way around.

[Richtee]

Actually it IS used in theatrics. Which is why I tried it in the first place. Concussion pot or some such name. Bought a "kit" a while back from Skylighter I believe. Minus the gun, as I have one.

 

On Edit: Skylighter's description. "Binary compound"

FX1064

Concussion Powder

Concussion powder creates a very loud explosion/bang and a small puff of smoke. It can be be used to make air bursts or in concussion pots. It should only be used in concussion-type flash pots (such as our FX0620 Concussion Pot), NEVER, EVER in weaker pots. This is a binary kit which comes in two bottles for safe shipping and storage. When the contents of the two bottles are mixed, one ounce of flash powder is created. Never use flash powder in a handheld device. The smoke generated by our flash powders has a very mild odor, and is generally not irritatating. Use with Sparkle Powder (#FX1030) to add white sparks.

------

 

BTW, no WAY would I use an OZ of the stuff. Their "pot" has like 1.5 inch walls...LOL! Also appears to be stainless.

 

I was just interested in the physics, wave prop and such.

 

But if deemed improper, just delete it if ya would.

[FrankRizzo]

Yes, FP is used in concussion pots to simulate cannon fire or explosions theatrically. Usually a medium grade flake aluminum (US Bronze 808 or Obron 10890) or magnesium is used, not the fine Indian or German blackhead.

 

The loudness difference is simple physics. The walls of a concussion pot provide more confinement than a paper tube, so the reaction between the components happens faster. Granted, the top of the bore is open, but the column of air that sits inside that bore provides plenty of resistance. Be aware that a 11g mix of 7:3 can generate pressures of over 50,000PSI when using fine pyro aluminum.

 

The kit sold by skylighter is strontium nitrate and magnesium.

[Richtee]

The loudness difference is simple physics. The walls of a concussion pot provide more confinement than a paper tube, so the reaction between the components happens faster. Granted, the top of the bore is open, but the column of air that sits inside that bore provides plenty of resistance. Be aware that a 11g mix of 7:3 can generate pressures of over 50,000PSI when using fine pyro aluminum.

Dang i was hoping it had something cool like tube resonance or interference/diffraction of waves involved. Ah well.

 

50K PSI for a half Oz? Wow. Like I mentioned the Skylighter kit uses an Oz. err... about 28 grams. But like you mentioned, it must be a slightly less 'hot" mix, plus the pot looks like it's dang heavy duty.

 

Thanks for the info Frank. I guess I never thought about the fact it's just a bigger tube first and foremost.

[hst45]

  Be aware that  a 11g mix of 7:3 can generate pressures of over 50,000PSI when using fine pyro aluminum.

Frank, that's quite enlightening. I knew that it generated quite a pressure wave, but I wasn't aware that it was quite that high.

 

For people not used to thinking in terms of pressure here's a comparison; that's roughly 15% OVER the maximum allowable working pressure of the .44 magnum.

[TheSidewinder]

OK, thread stays open. Theatrical use is a legitimate application.

 

There's considerable difference between a stage concussion pot and what the original thread proposed to use, however.

 

And I don't think that would ever make the stage. Not if *I* were the Producer, anyway.

[Richtee]

And I don't think that would ever make the stage. Not if *I* were the Producer, anyway.

Tell ya what... that thing has to be LOUD! You better be playing a big BIG house to touch that off. Jeez-sus!

 

Thanks for leaving this open... *I* learned something. Even if it was obvious and overlooked the simple answer... heh.

[r1dermon]

the atmosphere above the flash charge has mass, and given the burn rate of flash powder, it's enough mass to effectively "plug" the tube for enough time for the flash to build up a considerable pressure differential. when the atmospheric "plug" is blown out, the resulting pressure release creates an audible boom and shockwave. the larger the bore, the more air is displaced, the deeper the boom.

[mickyp]

Educational and very eloquently put.

the atmosphere above the flash charge has mass, and given the burn rate of flash powder, it's enough mass to effectively "plug" the tube for enough time for the flash to build up a considerable pressure differential. when the atmospheric "plug" is blown out, the resulting pressure release creates an audible boom and shockwave. the larger the bore, the more air is displaced, the deeper the boom.