4 replies to this topic

[Gazza]

Hi all; what is the most commonly used burst composition in large and small cat 4 shells in the UK?
I have been to quite a few public displays this November and have noticed that most commercial cat 4 shells, large and small, seem to use flash as a burst composition- you can see the white flash for a fraction of a second immediately as the shell ruptures. However, I have also noticed that some shells do not possess this momentary white flash at the centre of their burst, so I therefore assume that they contain some other type of burst comp, such as H3 or KP.
I am trying to replicate that satisfying sharp, deep boom in the bursts of my 5 in. spherical shells. I am currently using a KP (k. perc, lampblack, sulphur and dextrin binder) as a booster (in a flash-bag), with BP coated on rice hulls.
Is whistle mix used in commercial cat 4 shells?

NB: I am referring to star-shells, not flash-bang salutes (it is obvious that salute shells contain flash).

Edited by Gazza, 17 November 2007 - 11:08 PM.

[seymour]

Coat the rice hulls with KP. I know commercial shells use that burst extensively, particularly Chinese imports. Other bursts commonly use commercially do include Black powder and Flash powders. I do not think Whistle is used.

[BrightStar]

My understanding is that the smaller commercial shells and rockets of 1.75" to 3" often use a slow flash mix coated on rice hulls. This presumably uses a cheaper grade of aluminium than the ordinary percussive Dark Al mixes.

From 4" to 6", KP on hulls seems to be preferred and is about double the power of BP if well pasted. Above this size, (or for gently breaking 6" pattern shells) it is almost always BP on hulls, sometimes loaded damp to lock the stars in place upon drying.

For most of us perchlorate-starved amateurs, KP is much more expensive than BP, so we just resort to whistle and flash boosters with our BP coated breakfast cereals and seeds...

Edited by BrightStar, 18 November 2007 - 06:02 PM.

[Gazza]

What about H3- is it commonly used in commercial cat4 shells, given the friction-sensitivity issues surrounding chlorate?
From my experience with H3, it is not exceedingly sensitive to friction, but definitely more so than BP. Just as long as sulphur (and BP) is kept away from it, there should be no problems.

[Arthur Brown]

Consider also that all the compounds in the design have to be compatable. Perc stars are easier in this respect than chlorate stars meal powder stars preclude chlorate bursts unless they are separated perfectly. Consider also that some commercial fireworks may be a year old before they are fired so there are long term stability issues that don't affect the amateur builder who may only store a shell for a few days before firing it.