Bottom fused mortars

[AdmiralDonSnider]

I´m becoming tired of making lots of piped blackmatch to light the lift charge of my shells. The same applies to those small "containers" or lift cups, which are a common affix in round shells.

 

I´m trying to adopt some techniques which seem to be more common in the East, but which are used also in the western hemisphere for reloadable comet or bombette batteries particularly.

 

These are:

 

- bottom-fusing by drilling a hole into the side the mortar and using time fuse or blackmatch

- using a volume measured or weighted lift charge dumped loosely into the mortar (not encased in a container)

- a variant of this is described by Shimizu (see his lines about the Jap Starmines in FAST): the charge is filled into tissue paper and this is tied close to form some kind of "cartridge", which is the pasted with a BP slurry on the outside to improve the ignitability

 

To me these methods seem quite convenient, particularly where people are test-shooting shells (without any desire to invest time in making and attaching a leader and lift cup) or for use in finale chains, where bottom-fused mortars are easily connected with quickmatch for rapid firing.

 

I´m, however, in doubt about the following:

 

- do I have to use more lift than when a lift cup is used, or will the same amount work well? I figured that these cups form a bit of confinement and also keep the charge centered below the shell, helping the energy to be used efficiently. In contrast, a small amoung of charge could easily "get lost" in the bottom of a mortar, and could waste some energy. Could be terribly wrong however...

- shall the fuse point downwards or upwards? Placing a round shell in the mortar on its crossmatched timefuse "nipple" may actually harm or destroy the fuse...

[BJV]

I´m becoming tired of making lots of piped blackmatch to light the lift charge of my shells. The same applies to those small "containers" or lift cups, which are a common affix in round shells.

 

I´m trying to adopt some techniques which seem to be more common in the East, but which are used also in the western hemisphere for reloadable comet or bombette batteries particularly.

 

These are:

 

- bottom-fusing by drilling a hole into the side the mortar and using time fuse or blackmatch

- using a volume measured or weighted lift charge dumped loosely into the mortar (not encased in a container)

- a variant of this is described by Shimizu (see his lines about the Jap Starmines in FAST): the charge is filled into tissue paper and this is tied close to form some kind of "cartridge", which is the pasted with a BP slurry on the outside to improve the ignitability

 

To me these methods seem quite convenient, particularly where people are test-shooting shells (without any desire to invest time in making and attaching a leader and lift cup) or for use in finale chains, where bottom-fused mortars are easily connected with quickmatch for rapid firing.

 

I´m, however, in doubt about the following:

 

- do I have to use more lift than when a lift cup is used, or will the same amount work well? I figured that these cups form a bit of confinement and also keep the charge centered below the shell, helping the energy to be used efficiently. In contrast, a small amoung of charge could easily "get lost" in the bottom of a mortar, and could waste some energy. Could be terribly wrong however...

- shall the fuse point downwards or upwards? Placing a round shell in the mortar on its crossmatched timefuse "nipple" may actually harm or destroy the fuse...

 

Have you thought about using E-MATCH.

BJV

[Gunzway]

I generally bottom fuse my mortars when I'm doing the one shell or two at night. In my experience, lift cups do provide more confinement and when I have used them; the lift has been more powerful than just the lift powder being dumped into the mortar and the shell placed on top. But it's not very significant, a little extra lift when not using a lift cup to give it that extra distance/power but it's nothing drastic and I usually stick to relatively the same amounts of lift in both scenarios.

 

When putting the shell into the mortar, I usually attach a cotton string to the top of the round shell (the opposite pole to that of the time fuse) and gently lower it down into the lift so there's no damage done on the time fuse. I find bottom fusing my mortars to be definitely more convenient when you just want to test a shell or two and you don't want to go through the hassle of a lift cup and leader. Reloading is a bit of a pain and that's the downside to it, thus I only employ such techniques when testing a couple of shells.

[ropyro]

I have used the bottom fused mortar technique with no ill effect on the performance of the shell. There were some differences though from the quickmatch version: the shell was a lot more close to the ID of the mortar, there was a paper disc on top of the shell to keep it in place and the lift cup had some blackmatch fuses attached to ensure ignition.

Here is what I mean:

1. There is the shell

2. Now there is the mortar with a piece of quickmatch attached (I could have used bare blackmatch without any difference to the concept)

3. The inside of the mortar

4. Round shell with the blackmatch pieces attached

 

P.S. The shell was 60 mm.

Edited April 4, 2010 by ropyro

[dagabu]

 

 

- do I have to use more lift than when a lift cup is used, or will the same amount work well? I figured that these cups form a bit of confinement and also keep the charge centered below the shell, helping the energy to be used efficiently. In contrast, a small amoung of charge could easily "get lost" in the bottom of a mortar, and could waste some energy. Could be terribly wrong however...

- shall the fuse point downwards or upwards? Placing a round shell in the mortar on its crossmatched timefuse "nipple" may actually harm or destroy the fuse...

 

Actually, lift cups are a relatively new invention. You should have no problem getting the same lift from the same amount of powder. There are a few things that you need to consider before you do go this route.

 

1. Make a cupped bottom inside the mortar, it will help direct the lift and will waste less powder. It will also allow for the time fuse to extend out of the bottom and not touch the plug, damaging the fuse.

2. Be extremely careful when pouring new powder into the mortar, if there is a hot spot, it will flame out and give you horrible burns.

3. Use stout string to lower the shell, this will allow you to use the string as a tail and give you the ability to stage the position of the shell when it bursts.

4. Use a large pop rivet in the fuse hole. All you need to do is knock the stem out and insert your visco or black match into the hole to fire the next shell since the rivet will protect the mortar body.

 

D

[AdmiralDonSnider]

Thanks everyone for the responses.

 

1.) I´m not sue how a cupped bottom could be realized in standard fiberglas mortars; good point however. I´m still wondering if it really makes any difference in the efficiency of the charge whether the gases all originate from directly below the center of the shell or not. Other than that, Shimizu´s abovementioned"cartridges" also sound like an interesting option, which would improve the position of the charge and eliminate the necessity to deal with "free" (1.1) BP in the field. Anyone used such cartridges?

 

2.) This definately requires extreme caution. I try to avoid reloading anyway.

 

3.) I didn´t grasp the role of stout string as a tracer, sorry.

 

4.) good idea

 

I´m test shooting bottom-fused 3" chrysanthemums with 10% by weight tonight. Let´s see how it works...

[dagabu]

Thanks everyone for the responses.

 

1.) I´m not sue how a cupped bottom could be realized in standard fiberglas mortars; good point however. You make a cup from wood or better yet, epoxy and glue it to the bottom. The fuse comes in through the cup wall so the fuse hole has more protection. I´m still wondering if it really makes any difference in the efficiency of the charge whether the gases all originate from directly below the center of the shell or not. Other than that, Shimizu´s abovementioned"cartridges" also sound like an interesting option, which would improve the position of the charge and eliminate the necessity to deal with "free" (1.1) BP in the field. Anyone used such cartridges?

 

2.) This definately requires extreme caution. I try to avoid reloading anyway.

 

3.) I didn´t grasp the role of stout string as a tracer, sorry. The string is not a tracer, it acts as a kite string. They are used on all Japanese ball shells with letters and words as it helps correct the direction of the break.

 

4.) good idea

 

I´m test shooting bottom-fused 3" chrysanthemums with 10% by weight tonight. Let´s see how it works...

[AdmiralDonSnider]

For yesterday´s shots I carefully drilled 4mm holes in my fiberglass mortars and used 10% by weight of lift (3/4FA). I inserted visco.

 

I can only report that both shells worked like a charm, even without a cupped bottom, lift cup or quickmatch pipe.

 

I did not realize any decrease in lift height at all. The theory saying that a lift cup allows the grain to be used more efficiently has to be questioned at least. The lift hardly covered the whole bottom, but well...

 

For me this method is the way to go. Shells are conveniently lowered using the loop on top of the shell and a lenght of string.

 

What definately is recommended is to cover the mouth of loaded mortars with foil or cardboard plugs as seen at japanese setups. Sparks falling into mortars with uncased lift will easily lead to premature launches.

Edited April 7, 2010 by AdmiralDonSnider

[TheSidewinder]

@ Don: It was my experience that breech-fired shells like that were quite thrifty in their lift requirements. Using the Skylighter 2" plastic cans and the matched tubes, I could lift them very well with just under a teaspoon of 2Fg. Of course, these were designed to NOT be pasted, since they had a 1/16" clearance and "coasted" slowly down the mortar when I put them in.

[dagabu]

Don,

 

The Japanese also use hand lit stars thrown into the tube to light the lift charge. I have a video around here somewhere of it.

 

D

[AdmiralDonSnider]

Yeah, that thriftiness is a welcome feature. The shells were 70mm O.D. in standard 3" mortars. I bet I could go with 8%.

 

@Dagabu: I know the vid. I think the things are called Sindoro; didn´t know these are stars. Another method peculiar to japanese shooting... like the one with red hot metal :-). The pyro and his grenade launcher.

[Mumbles]

I can really tell the difference between somewhat confined lift and loose lift in mines. I make bag mines. I've noticed a fairly substantial difference between just having loose lift below the lifting disk, and having it confined in a baggy of some sort. It might just be an effect of relative volumes.

 

There is also a big difference if using somewhat weaker lift, where the extra confinement can help to increase the power. Higher temperatures and pressures lead to faster burning.

[Arthur]

Quality of fit of shell in mortar has a lot to do with lift economy. I put some six inchers in a mortar that they barely slid down and they were far too high, I could have used 30% less maybe 50% less lift, but that was with about 1mm all round so little gas escaped.

 

With loose lift I'd want to be very certain that the fusing was resistant to any local sparks or damage. If there is live QM crossmatching time fuse exposed then sometime there will be a crossfire with unfortunate results.

[AdmiralDonSnider]

Up to now I´ve only used the bottom-fusing technique for round shells. But what about traditional canisters with top fusing (spolette)? Here the delay element doesn´t contact the lift charge.

 

Will such a shell, with the spolette pointing upwards, light from the lift gases solely? I prime the spolette with the usual match and a generous NC-based meal slurry dipped in 5FA.

[dagabu]

Up to now I´ve only used the bottom-fusing technique for round shells. But what about traditional canisters with top fusing (spolette)? Here the delay element doesn´t contact the lift charge.

 

Will such a shell, with the spolette pointing upwards, light from the lift gases solely? I prime the spolette with the usual match and a generous NC-based meal slurry dipped in 5FA.

 

Tricky question.

 

Yes, a lot of garnatures are lit by the lift gasses but Maltese style shells (canisters) have a self sealing piston that effectively seals the tube as the shell is lifted and the bypass fire is minimized.

 

At club shoots, I drop four festival ball shells in the mortar on top of 8" ball shells. They are solely lit by the bypass gasses and lifted with the shell.

 

But the correct answer is no, the leader is tied into the spollette and then follows the shell down to the lift bag. The leader lights the spollette first and then the lift is lit.

[KruseMissile]

In FAST, shimizu talks about using something like a horseshoe that is red hot inside of a mortar, then you drop the shell,which has the lift inside of a tissue paper, into the mortar. Probably not the best idea but its a thought XD

[dagabu]

There is a video of a show where they are dropping a small chain that is red hot on top of shells that are already in the mortar. Ill see if Mike Swisher has the link.

[AdmiralDonSnider]

Tricky question.

 

Yes, a lot of garnatures are lit by the lift gasses but Maltese style shells (canisters) have a self sealing piston that effectively seals the tube as the shell is lifted and the bypass fire is minimized.

 

At club shoots, I drop four festival ball shells in the mortar on top of 8" ball shells. They are solely lit by the bypass gasses and lifted with the shell.

 

But the correct answer is no, the leader is tied into the spollette and then follows the shell down to the lift bag. The leader lights the spollette first and then the lift is lit.

 

I usually follow Fulcanellis style of finishing (nothing special or maltese), but as it´s said that everything "not under pasted kraft" is roasted anyway, I figured that it´d make no difference whether the charge or the delay fuse was lit first. Bottom fusing also here would eliminate the necessity of using leader, passfire, bucket and lift wrap. These are not my favourite operations in shellmaking...

 

I´m aware that the shell size is an important variable when talking about reliable ignition from the lift gases. But I´m talking about 3" and 4" shells mainly, where the gases do not have to travel a long "distance" to reach the centered fuse. When making an 8" shell, I wouldn´t try to save effort with leader and passfire.

[dagabu]

I never bottom fuse cylinders, it is almost impossible to fire proof a shell without a significant time commitment. I am a believer in conservation of time and resources so top fusing is the answer.

 

You should try the Maltese method once, it is superior to traditional Italian building IMHO.

[Mumbles]

All the scratching, match, and granular BP should be more than enough to ensure ignition. If you're worried, you can always put the spolette facing down. It's more risky of course.

[AdmiralDonSnider]

All the scratching, match, and granular BP should be more than enough to ensure ignition. If you're worried, you can always put the spolette facing down. It's more risky of course.

 

I shot four bottom-fused cans at NYE, all with spolette delays and all with fuses pointing upwards, having blackmatch bent over and tied, followed by an NC-based meal slurry and 5FA dip over the spolettes.

 

They lit well. No problems.

[sparks]

I use 1 1/2" tubes and bottom fire film canister shells with great success.....I hot glue card discs onto the canisters with 1/4 time fuse and seat them onto a piece of waxed paper for a good seal.

Also, on the 1" shots, I use a over seal of hard cardboard for bottom shot mines etc.

Still having a bit of a problem getting commercial results from my BP