Breach fusing

[mike_au]

I've done a bit of searching but I can't find much info on the advantages/disadvantages of breach fusing. Breach fusing doesn't appear to be terribly popular so I'm assuming there is something that makes muzzle fuses much better.

 

I'll try to summarize my theories and hopefully someone will point out if/where I'm wrong.

 

Advantages:

 

Requires less fuse

In the case of ematch, fuse isn't required and there is no plastic running down the mortar waiting to be melted

 

Disadvantages:

Lift powder would need to be exposed (no lift cup) to ensure ignition

Possibly weakens mortar

 

Is that about it? I'm planning on building a rack that will be fired by ematch and I was thinking of breach fusing it, are there any other problems to be aware of?

[TheSidewinder]

I'm on the way to work, or I'd answer this fully. I've done it with 2" mortars, and have a rack of four that I built for it. Breech-firing uses much less lift, too. There are a couple of extra precautions, also.

 

I'll get the specs for you tonight and post a more complete answer.

[Swede]

I'm interested too. With my tiny 2" and 1.5" mortar tubes, I think I'd rather breech fuse, and use preloaded lift bags.

 

The old muzzleloading cannons used powder bags, and once loaded, a bronze pick is used through the vent to pierce the bag, exposing the BP to the fire. I'm thinking that would work well for a small setup. You could have lift bags of various weights, 15g, 20g, etc, and tailor the lift bag used based upon the mass of the shell. And if you lift a shell too low, you can correct for the next one with a larger lift bag.

 

Loading shouldn't be a problem. I've heard (can someone verify this?) that even loaded upside down, the cross match will still take fire when the lift ignites... you get a good shell. Otherwise, I'd create some sort of tape loop, and use a length of string to lower the shell properly, then remove the string.

[tentacles]

There's info over on Danny's site about breech fusing (http://wichitabuggywhip.com/fireworks/mortars.html#bpc scroll up to the previous heading), he suggests making a small wooden plug for the bottom to serve as a permanent lift cup and get even more lift for your money.

[Bonny]

For all my 1" cylinder shells I just dump the powder in and drop the shell on top with the fuse down. I've also fired double shells and the lift gases easily light both shells (one fuse on bottom one fuse on top). I use visco with a blob of NC/BP slurry as prime, or dipped in NC and then meal D.

[Richtee]

For all my 1" cylinder shells I just dump the powder in and drop the shell on top with the fuse down. I've also fired double shells and the lift gases easily light both shells (one fuse on bottom one fuse on top). I use visco with a blob of NC/BP slurry as prime, or dipped in NC and then meal D.

That's ABOUT how I cooked my hand as you recall. HEaled up well, BTW.

[Bonny]

That's ABOUT how I cooked my hand as you recall. HEaled up well, BTW.

The fuse is through the side of the mortar into the lift, I think you misunderstood. the fuses on top and bottom are the shell fuses.

Glad to hear your hand is OK.

[TheSidewinder]

OK, for breech firing:

 

Over on Skylighter they have some mortars with a true 2" inside diameter. There are matching canister shells (plastic, two piece) that are 1-15/16" outside diameter. As you can see, there would be NO room for a QM passfire to the bottom of the shell.

 

The two-part cannister looks much like an oversized film can. The "lid" comes in two styles. One with a hole for visco, which is worthless IMHO. And another one with a hole sized for timefuse. This is the set I bought. You hotglue a piece of timefuse into the hole, then crossmatch what will be the inside end of the fuse. Fill the cannister with your ingredients. This is usually just mxed stars and burst. I used lightly powdered rice hulls as filler. Once filled, snap the lid in place, leaving a small gap. Run MEK or Methylene Chloride (?) around the rim and snap fully shut. Clamping it shut is a good idea. See the Skylighter for appropriate solvents to use for sealing.

 

Once fully dried, crossmatch the exposed end of the timefuse. Keep in mind that you will drop the shell with the timefuse DOWN, and it will rest on the end of the fuse, actually. So I personally recommend actually punching the fues and using either Thermalite, or good single strand blackmatch. If you have the 5-strand, blue plastic-wrapped QM, this is ideal as each strand is seperate and the perfect diameter to fit an awl-punched piece of fuse. I personally then dip the end of the fuse in some NC lacquer and GENEROUSLY powder it with good BP or commercial Fg or FFg. Let dry completely.

 

Mortar preparation: I used a hole-saw to drill four 2-inch ID holes in a length of 2x4, spaced about 6 inches apart, and glued the mortar tubes into the 2x4. I prepared the paper mortar tubes by soaking them in a 50-50 solution of Marine varnish (Valspar brand?) and isopropyl alcohol for a few minutes, then hung them to dry for a full week. After many, many firings, each tube looks pristine. If you don't coat the tubes they will have a VERY short life.

 

In each mortar, drill a slightly larger hole than the visco you want to use as "ignition fuse", approximately one inch above the end of the plug you used (or in my case, above the 2x4 "top").

 

Coat the hole in waterglass, at least once and preferably twice. This will insure the hole doesn't get too big.

 

To use:

 

Pour a lift charge into each mortar. It will take a LOT LESS than a standard lift charge for a 2" shell. I used a bare half-teaspoon. Insert a length of visco into the drilled hole, then drop the shell fuse-side down into the mortar, holding the visco so it doesn't "blow out" from the air pressure of the dropping shell. (It does happen: the shell seal is tight.) Once the shell is bottomed out, light the visco and retire.

 

The sound of the lift is unique. It's nowhere as sharp as a regular shell, and has a "popping" sound to it.

 

Experimentation with a dummy shell of the correct weight is a must, but once dialed in it won't vary much at all since there isn't really any way to make them except to just pour in your mix.

 

It's time-consuming because you MUST insure there are no residual embers in the mortar. After all, you're pouring in raw BP. Lift bags MIGHT work if taped to the bottom of the shell, but be sure the bags are thin enough to allow the visco to burn through them or you'll get a dangerous hangfire.

 

I had fun with these the first year I was in the hobby, but since it's so time-consuming I abandoned that in favor of traditional quick-matched shells in a regular mortar.

 

Hope that helped.

[mike_au]

Sounds good.

 

I'm in australia so I'm going to be making everything myself. It's not so much that I couldn't get a fuse down the side if I wanted to, it just seems much neater to have them come in the bottom. Plus it means I can have a shorter lead on my ematches.

[TheSidewinder]

Sounds good.

 

I'm in australia so I'm going to be making everything myself. It's not so much that I couldn't get a fuse down the side if I wanted to, it just seems much neater to have them come in the bottom. Plus it means I can have a shorter lead on my ematches.

 

Errr..... Ematches?

 

You really will have no practical way to use ematches when breech-firing.

 

If you make the side-hole big enough to slip the ematch head in it, you will lose a good deal of the the lift power, and the mortar will be giving one hell of a side-force out that hole during ignition. If you make the hole only large enuogh to accept the lead wires, you have to "fish" the wires from the inside out, and that will be all but impossible.

 

Breech-firing really only works with a visco ignition fuse. Thermalite would work, but that makes for a damned expensive ignition fuse...

[mike_au]

Aaah...fair enough

 

I haven't actually started making my matches yet, I assumed they would be a similar size to normal fuse :/

 

I guess I will have to rethink that design then.

[Richtee]

Coat the hole in waterglass, at least once and preferably twice. This will insure the hole doesn't get too big.

Hey Sidewinder-

 

Think a short hunk of small diameter thin metal pipe could be used to line the hole? Like an inch long and of the 3/32 ID type? Epoxied in of course. Something like the hobby brass pipe type stuff? Would prevent fuse hole erosion... or is waterglass just as effective?

[TheSidewinder]

I sure wouldn't use any metal, richtee.

 

The waterglass stops erosion dead. Use two coats as I suggested, letting each coat dry thoroughly. The mortars I made still look pristine.

[Richtee]

I sure wouldn't use any metal, richtee.

 

The waterglass stops erosion dead. Use two coats as I suggested, letting each coat dry thoroughly. The mortars I made still look pristine.

Thank you Sir. Will order some waterglass after the holiday.

 

Has many other uses too. And I like the efficiency of the breech load.

[moonshot]

I have used the breach load method to launch 1 3/4" home made cannister shells from a fiberglass tube I got out of a commercial 1.4g shell set. I drilled a hole in the side of the tube just above the end plug inserted a piece of visco fuse and made the lift charge from BP wrapped in news paper.I just bundled the lift charge around the time fuse on the bottom of the shell and pressed it down onto the fuse. This works fine for smaller shells.