39 replies to this topic

[BurlHorse]

I actually am not really worried about perfect breaks, I'm kinda more interested in the process of creating the shell, and launching it. Besides, anything that works even slightly will bring a gleam to my eyes, as I will know that I'm on the right track I might sit down and go through the shell building process with an inert filler as suggested. If anything it will prepare me for the real thing (sort of ). I will probably settle for commercial black powder, as my ball mill is not quite complete (stupid thing!). Wish me luck

Edit: Kinda on topic, but when you buy PVC pipe, is the size (50mm, 90mm etc) the internal or external diameter of the tube.

Guppy,

The PVC pipe over here in the good 'ol USA is mesured in inches, and if it's schedule 40 pvc the mesurement is the ID of the pipe.

Edited by BurlHorse, 11 February 2004 - 04:33 PM.

[Lil_Guppy]

If that means you are going to use PVC as the mortar, don't.

You'd probably get away with it for small shells, but it is not a good habit!

I actually want it to make a case former out of it. Don't worry, I do know that using PVC for mortar tubes is dangerous/lethal/suicide. Besides, I have my mortar tubes. Good ol' cardboard ones *shakes his head* and to think everyone thought I was going to make a mortar tube out or it But seroiusly, PVC pipe is nice and cheap, and I was going to fill it with plaster to make a former out or it. As for my question, I think I might just go to the plumbing store armed with a set of callipers

[alany]

I'd just leave it hollow, makes it much easier to remove the shell casing. I guess you could fill it and bore out a hole to match the spoulette, which is pretty common practice with timber formers.

When I go looking for shell formers I usually wander around the house the the mortar in one hand, looking for cylinderical things that fit the mortar with the usual shell wall, spiking, pasting and piped match clearance plus a little bit more for luck.

If your shell is under-sized you can always reconfigure the lift bag and fusing, adding a sabot of wadding. Works great with top-fused shells, I just put a branch in the leader to light the spoulette, tie a bag of pulverone to the end of the leader and tape a ball of wadding between it and the shell bottom. Takes less lift too, which is great if you lift is totally crap like mine is.

[BigG]

A good former can be made from a rolling pin. Look for a wooden one that got a loose axial running from one side to the other. You cut out the axial and you left with a former that has a hole running all the way through. Those pins come in verity of sized - from 30-60mm.

Edited by BigG, 12 February 2004 - 04:52 PM.

[BurlHorse]

HEHE, Stole my thunder G, I was going to tell him the same thing......

Regards, Stay Green,

Bear

[Phoenix]

My 40mm can shells (about 45g) take 3.5g of milld and pressed BP to lift them to about 25m (I think - I use a 2.5 second fuse and they break just before they arc over). 40mm round shells (about 16g) take about 2.5g to do the same. The mortars are about 35cm long.

In my small can shells, I have seen no difference in the break whether I arrange the stars carefully, with the break in the centre, or just mix it all up. Consequently, I now just dump a 50:50 mix by volume of stars and BP on vermiculite into the casing. Works OK. They are 33mm I.D and 37mm O.D. and usually between 6 and 8cm long.

I make them by wrapping two dry turns of cereal box, a little narrower than the finished shell will be long, around the former, and then following that with a strip of recycled kraft, cut to overlap by about 15mm at each end. This is pasted in the middle (where it is over the cardboard) but dry at the edges (which overhang). I then place an end disc in the outer kraft wrap, resting on the card liner. This is made from two glued together pieces of cereal box, and already has the spollete in place. I snip the outer wrap into strips and glue them down one by one. I let this dry, then fill it as solidly as possible my burst and star mix, and then put another disc on top and pleat that in place. I then spike it with cotton vertically, but not horizontally as it would be too wide for the leader, and because hose breaks annoy me.

(PS There is an article on 1-1/2" Insert Shells on Passfire, which are very similar to mine.)

[Lil_Guppy]

Ok... Just finished making an inert (no I didnt make a spelling mistake) shell. I ended up finding something 38mm (~1?in) in diameter to use as a former. After placing it (the completed inert shell not the former) down my mortar tube, I measured the gap between the walls of the mortar and the walls of the shell to be 4-5mm. Is this about right, or will the gap need to be a little bit smaller? I know that someone mentioned using a piston kind of thing, but I would like to try and make a perfect (if there is such a thing) sized shell. There will probably be 1mm less gap around the edges if I rolled the case liner with the kraft outside. The one I did just now had the liner inserted after rolling (because I forgot to roll it with the kraft ).

Edited by Lil_Guppy, 15 February 2004 - 08:21 AM.

[Stuart]

That gap is too large. If you do the maths, its like having a hole just over 10cm squared in your mortar which is quite a large gap. The fit wants to be snug so they just fit down the mortar, mabye with a little push.

Stuart

[Yugen-biki]

A tip to "shell beginners".

When I started makeing my first cylindrical shells I couldn?t get them higher then a few meters in the air. My problem were the gap (to large) and the lift charge. I foud out that when using green powder or similar the burning speeed (--> and the hight of the shell) gets higher using powdered or "coarse sand granule like" size on the lifting sharge. Green powder is not as explosive as real BP so the gap needs to be none to tops 1-2mm. (I were experimenting on 2 inch cylindrical shells). Using a cylinrical shell (40-60g) 2" with no gap (the shell were pushed firmly down) and 35-45g green powder granulated to 1-1,5mm the shell got a acceptable hight. (The delay/spolette were 1-2 seconds)

The shell it self is not as hard to not get good.

When using good BP lift charge the gap can be as big as 6mm (on both sides!!) on my 3" spherical shells. --> the gap is nothing that can be a fixed parameter. You have to figure that out by your self, but some guidelines are precent here in my post and in the forum.

When you have smelt the smoke from shells....

[pyrotrev]

An alternative to spiking with string is to use long thin strips of pasted paper wound horizontally and vertically, this seems to be the favoured method in Chinese factories making stuff for Italian companies, and it can give a creditably even burst. If you can't be bothered to mess with all the gluey stuff I guess you could try that old gummed kraft tape you sometimes see in art/stationary shops... though I wouldn't advise licking to moisten it, one's mouth might get a little dry after the first metre or so.....

Edited by pyrotrev, 15 February 2004 - 08:28 PM.

[BigG]

My 40mm can shells (about 45g) take 3.5g of milld and pressed BP to lift them to about 25m (I think - I use a 2.5 second fuse and they break just before they arc over). 40mm round shells (about 16g) take about 2.5g to do the same. The mortars are about 35cm long.

Thats using home made BP!?!? Amazing. I would never dream on getting insert shells 25 meters in the air using 3.5 grams of anything... More like 10-15. What procedure do you use to make the BP?

[Lil_Guppy]

Well... First of all, thanks for all the input and help guys. I constructed my first 'live' shell today, and launched it an hour ago. It was almost perfect (for me) Symetrical break, didn't hose or bow tie. The shell survived a really heavy lift charge, which I used to stress test my shell making and spolette rolling techniques. Spolette functioned perfectly, breaking the shell just on apogee. Here's what I did:

First, I rolled a case with a liner. Liner was cut from a sheet of A4 paper to give 2 turns around the former. Casing was cut from 65gsm kraft to give 2 turns around the former. I know that shells of this size may not need them, but I used end disks. Anyway, a hole was punched through 2 of the end disks so that the spolette fit nice and snug (one dist was used now and the other punched disk was used after the casing was pleated down). The spolette was rolled (with glue) around a BBQ skewer (small I know but I never had a failure during testing) to about 2mm-3mm wall thickness and dried. It was then rammed with a filed down nail of suitable diameter so that the spolette contained 13mm of BP and then rammed once with with a normal nail to gouge a nice V shaped notch in the passfire side to aid in ignition of the burst charge (NOTE: I had perfected the timings during my spolette tests).

I then coated (dont laugh) Rice Bubbles with meal powder to use as a filler. These were dried and half of them put into the shell. A handful of stars (thats all I had ) were put into the shell and the remainder of the shell was filled with my Rice Bubbles (snap crackle POP! ). Then whole thing was bounced around to settle everything. An end disk was added to the shell and the casing pleated down. Another end disk was added to each end (as per larger shell construction. Overkill I know, but the results were very good). I then spiked it with 8 verticals (no horizontal spiking was used) and then the pasted kraft wrap was applied. The shell was then placed in the sun to dry.

After drying, a simple lift cup was added to the shell on the spolette end. I know that this can cause problems, but I did not get any blow throughs during my spolette tests, most likely because of their small ID. The quickmatch was poked in through a hole and sealed with some hot glue. I then charged it with a heavy lift charge (11g of homemade granulated BP) and pleated it over and allowed it to dry. After drying it was taken out to my test area and launched, drawing ooo's and aaaaah's from my father, who thought it was a commercial shell

Just a quick note, the Rice Bubbles added a LOT of effect which made up for the small amount of stars. They left mini trails as the burnt which added to the effect. It also was a good indication of the break, which was fairly spherical, which I thought was very difficult to get with such small shells and BP as a burst charge.

Edited by Lil_Guppy, 17 February 2004 - 11:56 AM.

[BigG]

Well... First of all, thanks for all the input and help guys. I constructed my first 'live' shell today, and launched it an hour ago. It was almost perfect (for me) Symetrical break, didn't hose or bow tie. The shell survived a really heavy lift charge, which I used to stress test my shell making and spolette rolling techniques. Spolette functioned perfectly, breaking the shell just on apogee. Here's what I did:

First, I rolled a case with a liner. Liner was cut from a sheet of A4 paper to give 2 turns around the former. Casing was cut from 65gsm kraft to give 2 turns around the former. I know that shells of this size may not need them, but I used end disks. Anyway, a hole was punched through 2 of the end disks so that the spolette fit nice and snug (one dist was used now and the other punched disk was used after the casing was pleated down). The spolette was rolled (with glue) around a BBQ skewer (small I know but I never had a failure during testing) to about 2mm-3mm wall thickness and dried. It was then rammed with a filed down nail of suitable diameter so that the spolette contained 13mm of BP and then rammed once with with a normal nail to gouge a nice V shaped notch in the passfire side to aid in ignition of the burst charge (NOTE: I had perfected the timings during my spolette tests).

I then coated (dont laugh) Rice Bubbles with meal powder to use as a filler. These were dried and half of them put into the shell. A handful of stars (thats all I had ) were put into the shell and the remainder of the shell was filled with my Rice Bubbles (snap crackle POP! ). Then whole thing was bounced around to settle everything. An end disk was added to the shell and the casing pleated down. Another end disk was added to each end (as per larger shell construction. Overkill I know, but the results were very good). I then spiked it with 8 verticals (no horizontal spiking was used) and then the pasted kraft wrap was applied. The shell was then placed in the sun to dry.

After drying, a simple lift cup was added to the shell on the spolette end. I know that this can cause problems, but I did not get any blow throughs during my spolette tests, most likely because of their small ID. The quickmatch was poked in through a hole and sealed with some hot glue. I then charged it with a heavy lift charge (11g of homemade granulated BP) and pleated it over and allowed it to dry. After drying it was taken out to my test area and launched, drawing ooo's and aaaaah's from my father, who thought it was a commercial shell

Just a quick note, the Rice Bubbles added a LOT of effect which made up for the small amount of stars. They left mini trails as the burnt which added to the effect. It also was a good indication of the break, which was fairly spherical, which I thought was very difficult to get with such small shells and BP as a burst charge.

Well done. Spollette-End fusing will work fine for shells under 2-2.5 inch. Above that, and you might run into problems.

I usually don’t bother with attaching lift charge to such shells, so they can be utilized as insert shells when needed. Instead - I just use a lift charge placed in a tissue paper. The mortar is pierced at the bottom, a fuse is pushed through, a lift charge is drop and on top of it – the shell.

One thing to note – Nail sounds like a strange way to do spollette. Go buy a 6mm aluminium rod and cut it to size. Much easier.

Edited by BigG, 17 February 2004 - 12:08 PM.

[Lil_Guppy]

I usually don?t bother with attaching lift charge to such shells, so they can be utilized as insert shells when needed. Instead - I just use a lift charge placed in a tissue paper. The mortar is pierced at the bottom, a fuse is pushed through, a lift charge is drop and on top of it ? the shell.

I know, but I probably wont go any bigger till I do a few of these shells. Plus I wanted to make a nice, clean, neat unit that could be just dropped in the mortar tube and lit

[Phoenix]

BigG said,

I usually don?t bother with attaching lift charge to such shells, so they can be utilized as insert shells when needed. Instead - I just use a lift charge placed in a tissue paper. The mortar is pierced at the bottom, a fuse is pushed through, a lift charge is drop and on top of it ? the shell.

That's probably another reason why I get away with using very little lift charge - I make a rather sturdy lift cone and paste it onto the bottom of the shell, to provide a bit of containment, like a Maltese lift maroon. Another advantage I see in these cones is that they are less likely to be fired by any smoldering debris in the mortar. Of course, if you only use tissue, there isn't likely to be a lot of debris left, and in such small shells the consequences of one firing whilst you were next to it (not over it) would not be too dire (you probably wouldn't be concussed by the muzzle blast). Each to their own

Edited by Phoenix, 17 February 2004 - 03:08 PM.