Siegmund Posted February 15, 2012 Posted February 15, 2012 I know it has already been said, in general terms, that we can't be 100% confident of the details in those documents posted last summer with the details of a bunch of Chinese cakes. Still, I was browsing them earlier this week, and was surprised to see that almost all of these claimed to be using an unusual burst charge: 40% KP40% metal (25 magnalium and 15 aluminum, or vice versa)20% sulfur Really? I know that people talk about 50-50 as 'slow flash', compared to 70-30. Is this just taking that a step further, so slow it can be used as burst and not shatter stars? (Would it even work? Can't remember ever seeing a comp that had less oxidizer in it than fuel before: the few star comps that are less than 50% oxidizer have big percentages of nonfuels like strontium carbonate in them.)Even if it did work, would it make any sense to use up that much aluminum when it's so much more expensive than the ingredients in a normal burst mix? Is it a deliberate desire to make a white flash at the burst rather than just light and eject the stars without calling attention to the burst?
Arthur Posted February 16, 2012 Posted February 16, 2012 Shell size makes a huge difference to the compounding! It's not unusual for a BP lift system to need boosting for small shells or inserts. Typicaly with a BP on hulls burst powder lots of booster would be used for a 1" insert less for a 2" less for a 3" then probably no boost for a 4" and greater.
Potassiumchlorate Posted February 16, 2012 Posted February 16, 2012 I use standard flash (70:30) to my 2" shells. It works very good.
Mumbles Posted February 16, 2012 Posted February 16, 2012 If I remember correctly, most of those cake data sheets were for bombettes or small cylinder shells. It'd be hard to really say if that formula is real, or of bursting with straight flash would work particularly well without experimenting. A friend of mine dissected and fairly well recreated the hard breaking class C cylindrical shells that have been going around the US lately such as excaliburs, black mambas, and the likes. He got it to work the closest by using mostly BP and some fairly strong flash. These didn't have that tell tale bright white break that some cakes I've seen have. I don't recall how the real deal class C shells break. It could be that the slower flash allows you to use straight flash. I've always gotten better results personally by using both BP and flash. Something to this effect was mentioned in another thread by FlaMtnBkr. Well, he mentioned that he broke his shells with 5g of hot flash, but seemed to forget about the 80g of BP that is also in that shell. There is 80g in there at least for the method I've seen by the same well respected instructor. You'll never know until you try I guess. Even if it does work using straight flash, I'd still personally feel more comfortable and confident using BP with a smaller amount of hotter flash.
nater Posted February 16, 2012 Posted February 16, 2012 I opened up a damaged premium consumer cylinder shell last year. It was soaked in water, but the burst appeared to be flash with bright aluminum with granulated BP and small rolled stars. The stars were tossed into the burst randomly and there were no hulls. Each end had a thick clay plug and visco was used as time fuse. I didn't burn the burst as it was wet and I am cautious with the unknown contents of a well performing product. In any case, the construction explains the sloppy, hard breaks these style of shells are known for.
FlaMtnBkr Posted February 16, 2012 Posted February 16, 2012 Yeah I didn't mention any of the other details as I was only pointing out a legitimate use for flash. And that 5g works good for a 4" plastic shell in a flash bag. I would imagine you would tone down the amount as you make smaller shells. But based on some of the over filled class C stuff, maybe not. Some of them break more like a salute with stars than a small shell. There is a member on passfire that mainly makes 1 3/4" shells. He uses a kp based burst on hulls with a whistle boost. He claims to have tried many different types of break and says that is what gives him the biggest break. I don't know, but the size of the break may not depend on the power or speed of the break charge. It might depend on allowing the shell casing to build up the highest pressure inside before bursting. If that were the case then I would think the burst would need to be tuned to the shell size and the way it is made and the materials it is made from. So you may need to just experiment with different break and boosters for the shells that you make, and there is no simple answer as to what is best for a certain size shell. Just a thought.
pyrojig Posted February 16, 2012 Posted February 16, 2012 I too have made many 1.75 festive ball shells in my years of pyro. They are fun ,simple, cheap, and you can make a ton of them in no time. They are nice as filler shells in a show. I have had really good luck with just simple riced bp spiced with whistle. The thing that is more critical is a balance of burst v.s. pasting (or spiking etc.). More power = less paste v.s. weaker burst charge needing more pasting. I believe that Shimizu had a good section on this in F.A.S.T. .
Recommended Posts