Stacking fireworks

[ryanlg95]

I am planning on doing a very small show (3 - 4 shells) but I only have one mortar, and I don't want to be reloading it due to speed.

It it possible to stack 2.5" canister shells on top of each other, maybe with cardboard shock resistors in between, and would it cause any damage to the shell underneath.

Thanks

[NightHawkInLight]

Both shells will go off at once, or more likely it will just blow up the gun. Is it really that big of an issue to reload one mortar three or four times?

 

You could also just go buy some PVC pipe and bury it to use as your mortars. PVC should not be used above ground because it can shatter, but it's fine if the majority is below ground. You don't even need an end cap on the bottom of the pipes, the dirt will handle closing it off just fine.

[ryanlg95]

Hi NightHawk,

I don't see why it would set off both at the same time. If you shoot sequentially from the top to the bottom, and maybe protect the leader fuses would it still set off both?

Thanks.

PS. I love your videos!

[nater]

i would feel more comfortable piggy backing shells than I would using mortars with no plugs. i was at a shoot last year where piggy backing shells was tested, and some myths debunked. I wouldn't be willing to call the practice "safe" but if you plan your distances safe you will be fine. In fact it is not uncommon to throw small unlifted shells on top of larger shells to create a layered effect.

 

Be warned, both shells -will- light at once. it is possible the gun will blow, maybe more so with canister shells than ball shells, but most likely they will launch together.

 

If your mortar is HDPE, be careful reloading it. 2 or 3 shots should be fine, much more than that and the tube could get soft with repeated firings. If you are only lighting a handful of shells and have the one mortar, just take it slow and reload. make sure there are no embers in the bottom, check and recheck before reloading.

[nater]

edit,

 

i gurantee you they will both light if they are stacked. EVERYTHING flammable in the gun will ignite. the whole mortar is filled with fire along with a 15 foot tall flame coming out of it before the shell even moves. it is only an instant, but these gasses are what propels the shell out of the run.

[ryanlg95]

Thanks guys

[Arthur]

A couple of extra mortars seems a wise investment! Properly made, properly plugged tubes are cheap especially compared with a visit to hospital, or a visit from your law enforcement.

[dagabu]

edit,

 

i gurantee you they will both light if they are stacked. EVERYTHING flammable in the gun will ignite. the whole mortar is filled with fire along with a 15 foot tall flame coming out of it before the shell even moves. it is only an instant, but these gasses are what propels the shell out of the run.

 

I have video of this effect somewhere on my PC from 2010 where we blew up some racks with different types of "mistakes" in loading. Putting color shells in upside down, putting two shells in the same mortar and putting a salute upside down in the mortar. Imagine you know how the last one turned out, everything splintered!

 

The two ball shells in the same mortar was a surprise for us all. If one were to take the lift charge off the bottom of up to three 3" ball shells and put them on top of a lifted shell in the same mortar, they would all leave the gun and would return to the earth before going off. Kind of scary.

 

BUT! If one were to drop a shell that is lifted in the bottom of the mortar and then placed a second lifted shell in the mortar and you lit the top shell first, an interesting thing happens (Total Hypothesis Warning!): The top shell lifts out of the mortar but the blast wave that carries the flame to the bottom shell which causes the lift charge to ignite and lift the second shell also increases the pressure in the mortar and the second shell has to overcome the additional pressure resulting in the HDPE mortar to swell and part causing the second ball shell to do a round trip and open on the ground.

 

The interesting part of this is that it is really hard to reproduce the effect as the lighting of the second lift charge has to be timed perfectly and only e-matching both shell to light at the same time would reliably blow the mortar each time.

 

Food for thought.

 

-dag

[nater]

^^

 

The test I saws was much less complicated. 3" shells, bottom lifted and ignited as normal, with more shells piggy backed on top. I think it was 4 shells total when the mortar failed. Some broke low, but not on the ground.

 

If I were repeating the experiment, I would ignite the bottom shells as normal. Then add more effects on top with any lift cups removed and the lift dumped into the bottom of the mortar. There is a point where the mortar would over-pressurize, one would just have to figure out where this is.

 

The practical side of this would be a cheap way to explore various rising effects with commercial product. A cup of stars for a mine to break, 3-4 3" shells piggybacked on top of a 6", saettines as a rising effect, and so on. We had experimented a little with this on some shoots a few years ago, then I recently read an article in an older edition of pyrotechnica which heavily promoted the use of such "parasite" effects and even had tables with different ideas and amounts.

 

With my personal risk assessment, this all is in the realm with experimental shells and probably not appropriate for use in any structured display until you are positive what the results will be.

[Arthur]

If these go as you hope (singly!) then they will NOT go as intended because the top one will only be a little way into the mortar and the others will be further down. SO the top one will get out rather limply and the rest getting better to the bottom. However the chance of 5 separate quickmatch leaders being perfect after some have fired is in reality NIL. There is a risk of fire passing to other leaders as the first shell lifts, there is a risk of the first lift crushing and splitting one of the other lift bags -firing that shell as well, with two or more lifts going at the same time there is too much chance of the mortar tube bursting ot losing it's bung. Please simply take your time and fire singly, or get enough tubes to use each one once only.

[nater]

If these go as you hope (singly!) ...

 

Won't happen. (not calling you out Arthur, I get the point of your post)

 

Take note starting at 4:30 in this video. Make sure to see the flame, the muzzle blast, and the shell finally leaving. Nothing flammable inside the mortar will stay unlit.

 

[dagabu]

The practical side of this would be a cheap way to explore various rising effects with commercial product. A cup of stars for a mine to break, 3-4 3" shells piggybacked on top of a 6", saettines as a rising effect, and so on. We had experimented a little with this on some shoots a few years ago, then I recently read an article in an older edition of pyrotechnica which heavily promoted the use of such "parasite" effects and even had tables with different ideas and amounts.

 

There are standards that deal with shells that are not fireable at showtime and the correct disposable methods. That said, I have been on site several times where we have had a case of 3" chi-com shells where the leaders pulled out, the lift cups were damaged or the combination of both, we simply threw three 3" shells in on top of 8" shells after pulling the lift cups off them and dumping the BP down into the mortar to be rid of them and when fired, the three 3" shells traveled all the way up as far as they normally would and broke in unison.

 

The balls shells just slide along the mortar and are ejected with the primary, the extra lift compensates for the extra weight.

 

Don't use loose stars, put them into t mine gab or plastic baggy on top of the shell, the shell needs to get moving and the gasses need to propel the stars out just ahead of the shell. If the shell moves first and the stars are already jammed in between the shell and mortar walls, the mortar will be damaged if not fractured, or as already said, the "bung" will be blown out.

 

It is also not allowed by the standards and is not done commercially due to the danger to the audience.

 

-dag

[Arthur]

My point being that there are two ways this will go and both are unsafe, so don't do it. Displaying something to your friends MUST be safe -they are your friends -you don't want to hurt them!

 

If you use one tube and reload you will have to remove all the debris from the bottom of the tube before you reload.

[cogbarry]

I have used the "piggy back" method to clear a mortar of a shell that failed to lift and no longer had a reachable quick match if any. It's done often but isn't considered safe. I'd make sure no one was near it (including yourself) when using this method. The method is simple and when I've done it/seen it done, the same size shell was simply loaded on top of the failed shell. The lift from the top shell lights the lift of the bottom.

 

"peanut" shells are basically two "piggy backed" shells. In NH, they are not supposed to be fired from above ground mortars, the mortars are supposed to be buried. This is one of those rules that is not commonly enforced and often broken.

 

Bottom line, don't light the QM, have a visco leader so you can get away or don't do it. Of course it's not safe unloading a mortar with a shell stuck in the bottom either, technically, you're supposed to flood gun with water, at least in NH. There's reality and there's what you're supposed to do. I've been in situations (i.e, the QM had gotten damp from humidity, was smoldering, and a string of 5" shells were failing ...or going off ten minutes after the QM was lit) where flooding the guns and destroying the shells was the only safe thing to do.

 

I definitely wouldn't design my show around stacking multiple shells in the gun. The top shell will fail to lift to a safe height due to incomplete combustion of lift and it will likely light the shell(s) under it. Not a good idea. Buy some mortars and build a safe and stable rack.

[nater]

As I said above, I would not call piggybacking shells "safe". I have never noticed the shells breaking low thoug, or at least low enough to be dangerous. Per NFPA 1123 multiple break shells are supposed to be shot in steel mortars. Peanut shells are multiple break, but I have frequently shot them in fiberglass or HDPE without incident.

[pyrojig]

 

 

Don't use loose stars, put them into t mine gab or plastic baggy on top of the shell, the shell needs to get moving and the gasses need to propel the stars out just ahead of the shell. If the shell moves first and the stars are already jammed in between the shell and mortar walls, the mortar will be damaged if not fractured, or as already said, the "bung" will be blown out.

 

 

-dag

 

This brings up a interesting point . When making "drag rope's " for shell orientation, the same prob could happen( as the stars). The shell could become jammed in the tube and cause probs. I guess one way to avoid this is to leave the rope out the top of the tube. Most shells, like some 8" that I have shot with effects attached, the rope is placed in the pipe. I never have witnessed a prob, but for a amateur using a off sized rope I'd imagine this may present a issue.

[NightHawkInLight]

The rope is pushed forward by the escaping gas perhaps faster than the shell itself. I very much doubt it would ever get wedged between the shell and the gun. Too much gas rushing around the shell that would keep it away.

[pyrojig]

The rope is pushed forward by the escaping gas perhaps faster than the shell itself. I very much doubt it would ever get wedged between the shell and the gun. Too much gas rushing around the shell that would keep it away.

Thats what I thought, but i guess in some special circumstances, there may be a chance. Im sure it would be that 1 in a million. But when dealing with amateur shell building ,there are too many factors/variables that can create dangers.

[cogbarry]

As I said above, I would not call piggybacking shells "safe". I have never noticed the shells breaking low thoug, or at least low enough to be dangerous. Per NFPA 1123 multiple break shells are supposed to be shot in steel mortars. Peanut shells are multiple break, but I have frequently shot them in fiberglass or HDPE without incident.

 

Piggybacking two shells has never caused a low break for me, not that I've done a lot of this. However, I think stacking (4) shells with spacers in between would bring the top shell's height up substantially. That will cause a low break.

 

Edited to put my response below the quote.

Edited March 19, 2012 by cogbarry

[dagabu]

As I said above, I would not call piggybacking shells "safe". I have never noticed the shells breaking low thoug, or at least low enough to be dangerous. Per NFPA 1123 multiple break shells are supposed to be shot in steel mortars. Peanut shells are multiple break, but I have frequently shot them in fiberglass or HDPE without incident.

 

True that but adding unlifted shells of one layer or less (whatever that means) of shells that are not less then 1/4 the diameter but not more then 1/2 the diameter of the parent shell, occupying less then 75% of the mortar tubes diameter may be lifted by the parent shell and lift charge. These are not considered to be multibreak shells. The unlifted shells will be centered in the tube by the parent shells lift charge and will not even touch the mortars walls when lifted.

 

-dag

[ryanlg95]

A bit of a bump, but how do Roman Candles fire multiple shots with out igniting the shot below them? Can't that be used in a mortar to have multiple shells in there?

[Mumbles]

Before you get your hopes up, you should know that roman candles use a much longer tube. A 2" mortar is maybe 12" long. A 2" roman candle is about 3 feet long or so. You still need the length above the shell to get them lifted to the correct height. Using a 2.5" mortar with even two shots would lower the effective length from 15" to about 9 or 10". It might work, but you'd have to over lift the top shell, and you could never go over 2 shot.

 

Anyway, there are two ways that large bore roman candles are made. The smaller ones are made a bit differently, but I wont go into that. The first way is to use a long length of visco to provide the delay. A load of lift is dropped into the bottom of the tube and the shell is dropped over the top. Then sawdust is poured on top and tamped down to ensure a solid plug. Most people generally do this in at least 2 increments of saw dust. For 2" ID candles 2 increments of 1/2c of saw dust is about right. The sawdust will need to be relatively fine. I pass mine through a window screen to remove the large pieces. After you have a solid plug of sawdust I drop a cardboard disk on top of the sawdust, though this is optional. I do this to prevent mixing of the lift and sawdust especially during handling and transport. Repeat this as many times as you'd like to maintain a proper lift height above the final shot. The top shot can be sealed in with a cardboard or chipboard disk or plug. Some also like to put a gerb or mine on top.

 

The other way to make it is fairly similar. Instead of sawdust a thick wad of felt is used with a piece of timefuse or a pellet of composition glued into the center. You can't just use felt from a craft store. This requires a much thicker felt. A wad of many thinner stuff doesn't work as well I've been told. You're looking at 1" thick pads of F7 to F12 felt I've been told. Neither are super cheap. 1" thick F5 from McMaster-Carr is about $60/sq ft. In full rolls, which are 10' x 6', it's about $25/sq ft. F 13 seems to be about $12/sq ft. You can potentially use them over again however.

[optimus]

Also see here for the plastic version of the large bore Spanish candles. These are from plasticos gamon and are designed to use with 10mm Martins & Martins timefuse. These work with no wadding.