Suitable Burst For 4" Round shells

[The-T]

Im planning on building some 4" shells, and I want to get a decent break that has some "oomph" to it. I was thinking of adding maybe 1-2 grams of flash booster (Either Kno3/Mg or Kclo4/Mg) my question is, will this flash comp. be able to withstand the force of the shell lifting without it igniting, resulting in flowerpot? Edited September 9, 2008 by The-T

[mike_au]

I'm in no way an expert on flash, but I seem to recall reading that KNO3/Mg was more reactive than KNO3/Al and could spontaneously ignite in the presence of moisture, also the reaction couldn't be easily prevented (like you can with boric acid with Al).

[Arthur]

Bursts can be assisted by a flash bag, but permanganate flash is too sensitive for this use. Too much flash and the shell will just break up in the sky and the stars may just fragment - rather spoils the effect!

[Bonny]

You could also use whistle mix as a booster. I've only made 3" shells so far and it seems to work well on those.

[Richtee]

Here's an experiment I'm trying with 3" shells:

 

What I did is made a plug recessed .25 inch inside the tube. The plug is BP with a bit of baking soda and ALOT of dexetrin. I cut small slots for a couple primed chunks of flying fish fuse in it. This allows the time fuse underneath to light the ends of the fuses and the slower BP delay plug. Bottom of tube is glued over time fuse stub. On the "top" side of the BP plug is about 2 G dark Al/Perc.

 

Theory: Time fuse ignites BP delay plug and fish fuse. Fish fuse spatters all kinds of stuff inside shell for a short time, igniting all stars. Delay burns thru to flash mix...ka-Blooie! A nice break, and good spread. I hope. Will report back.

[The-T]

You could also use whistle mix as a booster. I've only made 3" shells so far and it seems to work well on those.

 

Yea, I guess ill just use whistle mix for awhile.

 

@Richtee, Very cool idea, cant wait to hear the results!

[FrankRizzo]

Richtee,

 

I had a similar idea a while back, light the stars first, then trigger the burst charge. I used a tissue paper "baggie" of burst powder centered in the shell and a small circle of cardstock placed above the timefuse to direct the fire out to the sides. The problem is that the prime on the stars, and even the star comp itself releases enough gas and/or heat to cause the shell to begin bursting before the charge can ignite. The casing will fail in expected ways and cause poor patterning.

[Richtee]

Richtee,

 

I had a similar idea a while back, light the stars first, then trigger the burst charge. I used a tissue paper "baggie" of burst powder centered in the shell and a small circle of cardstock placed above the timefuse to direct the fire out to the sides. The problem is that the prime on the stars, and even the star comp itself releases enough gas and/or heat to cause the shell to begin bursting before the charge can ignite. The casing will fail in expected ways and cause poor patterning.

 

Sigh JUST experienced that. Was not thinking about the 2-3 g or so of coarse BP prime. BUT I did get a nice short delay salute...something eh? Then I seen half the stars in close prox get blown out. Sigh... back to the drawing board.

[spitfire]

In my opinion it is quite important for the ignition and breakpattern of a (4'' and >) round shell that it is ignited in the center of the shell.

Either if i use a flashbag, whistlemix or whatever. ignition at the wall of a shellcasing just ain't doing the trick for me. It may work with smaller diameters and/or stronger bursts like flash though. Haven't tried that with small round shells. Personally i prefer extending my timefuse or spoulette with a small paper tube filled with pieces of blackmatch. The tube being long enough to reach the center of the shell.

Edited September 23, 2008 by spitfire

[Chris]

In my opinion it is quite important for the ignition and breakpattern of a (4'' and >) round shell that it is ignited in the center of the shell.

Either if i use a flashbag, whistlemix or whatever. ignition at the wall of a shellcasing just ain't doing the trick for me. It may work with smaller diameters and/or stronger bursts like flash though. Haven't tried that with small round shells. Personally i prefer extending my timefuse or spoulette with a small paper tube filled with pieces of blackmatch. The tube being long enough to reach the center of the shell.

 

 

Absolutely. For a symmetrical break, the ignition has to spread fast throughout the burst. I basically adapt two techiques for different types of shells. If I want a symmetrical large break for a 3" or 4" shell, I use KP as the break charge. I also have a cannule going from the end of the time fuse to the centre of the shell. This is filled with either flash or granulated black powder. The choice isn't critical in 3" shells, but the need for a quick thorough ignition provided by flash grows as the shell size grows. This method however necessitates a good pasting job. I though I could mention that this is only suitable for paper shells, if you want a perfect pattern that is.

 

Another method for quicker construction is using flash powder as a booster. It is important to get the burst to light from the centre, but unlike with KP, flash will spread fire in the shell very quickly. Now, a small secret . Wether you build paper or plastic, if you use enough flash, you can completely skip pasting or hazzling with solvent. This is a technique we utilize at the company for some shell types, like round 4" polyps. For some traditional shell builders, this might seem very unorthodox. You must however make sure that the seam is very tight. Three to four tight wraps of masking tape round the joint should do. The advantage of this technique is that pasting can be skipped. On the other side, each shell eats up a litle bit more flash than normally.

 

I'm not implying that the last technique should be used solely. It gives a very hard large break, but unless your stars have got what it takes, you might end up with just a flash. Whatever works for each individually comes probably somewhere between heavy flash usage and heavy pasting.

Edited September 23, 2008 by Chris

[spitfire]

Three to four tight wraps of masking tape round the joint should do. The advantage of this technique is that pasting can be skipped. On the other side, each shell eats up a litle bit more flash than normally.

 

I'm not implying that the last technique should be used solely. It gives a very hard large break, but unless your stars have got what it takes, you might end up with just a flash. Whatever works for each individually comes probably somewhere between heavy flash usage and heavy pasting.

 

 

I have seen this method in German shells and rocket headings from ZINC GmbH. They just dumped stars in the shellcasing, and a soft plastic tube filled with flash was mounted straight on the timefuse. All that was left was closing the shell and apply tape around the joints. I understand that is simular to what you're saying..? This method asks for high quality stars, prime, and so on. May be worth trying one day.

[Chris]

I have seen this method in German shells and rocket headings from ZINC GmbH. They just dumped stars in the shellcasing, and a soft plastic tube filled with flash was mounted straight on the timefuse. All that was left was closing the shell and apply tape around the joints. I understand that is simular to what you're saying..? This method asks for high quality stars, prime, and so on. May be worth trying one day.

 

 

Yeah, Zinc makes shells this way.