Cylinder shell break symmetry

[greenlight]

I am quite new to actual shell building and tested a few 3 inch D1 cylinder shells last night.

I am having trouble getting good break symmetry and have uploaded a couple of mid break photos to show.

 

I am using 4:1 meal coated rice hulls as the burst with a small amount of benzoate whistle in the centre around the end of the spolette.

 

What is the best way to finish 3 inch cans for good breaks?

Rinfasciature with two sets of spiking or one spiking layer and then pasted kraft afterwards before lifting and leadering.

 

Should I start coating the twine in PVA glue before spiking?

[NeighborJ]

A symmetrical break is accomplished by the combination of proper burst charge, consistent star size, good priming-even with D1, centered placement of TF or spollette. IMO the pasting method and spiking pattern are the least of the concerns, provided they are done at least close to correct.

 

The problem I see in the pictures looks to be from either incomplete star ignition or inconsistent star sizing. It is very important to ensure that the entire star surface takes fire before the shell opens, a good layer of screen mix BP will solve this. If only a corner of a star lights it will never light entirely as it travels thru the air, it will loose mass slower than the other stars which means it will travel further and distort the break.

 

I have broken shells with MCRH but I prefer strait BP because of its pushing power. MCRH is fast and explosive but I've found it to lack that push needed to propel the stars very far- that's not to say that it couldn't, but a ratio of 7:1 may work better.

 

Jason

[greenlight]

Thankyou for your reply,

I will make another two 3 inch shells and make sure the stars are cut as even as possible and step prime them this time.

 

I will fill in all the gaps of the rice hulls with granulated BP as well and see how that goes.

Next batch of hulls I will try the 7:1 ratio. It is hard to manufacture large amounts of black powder where I live so thats why I was using the hulls as I only have a dual 3lb mill.

Thanks again for the input.

Edited October 9, 2017 by greenlight

[NeighborJ]

Well, step priming is a bit overkill, just an even coat of screen mix BP will do for a prime on that star.

 

Mixing the granulated BP with the MCRH could possibly be detrimental to the symmetry. There is a high likelihood that there will be some settling between the different size hulls and grains. If you want to conserve the limited amount of hot BP you have it is common practice to place the hottest burst in the center(in a thin paper sleeve) then fill the void between the burst and stars with the slower granulated screen mix. This method works great and will save your milled BP for its best use.

 

I believe Paul Moulder made a youtube video of this technique, I'll search and post it.

 

Jason

[Carbon796]

BP should be used for the canulle.

Polverone should be used for filling the intricacies between the stars.

MCRH are for ball shells.

Your twine should be saturated with wheat paste, not just coated.

 

Type of burst, paper, twine, spolette timing, and or spiking ( plus more ) can all have effects on burst strength / symmetry. Dont forget that cylinder shells burst in a radial pattern, while ball shells are a spherical pattern. The first pic really doesn't look bad at all. A video would probably be more telling, on what your burst is doing. Its somewhat on " edge " the stars pointed down are naturally going to travel farther and straighter. Than the ones pointed up, which will have to fight against gravity, will be shorter and be more prone to arc over. Specifically with a weaker break . . .

Edited October 9, 2017 by Carbon796

[Aspirina]

looking at the second pic, seems like you dont have a strong break... I think that if you use another break charge you might be to have a better simmetry. Another reason can be the filling of your shells, I only have experience with can shells and the simmetry improve a lot with this two tips:

- Fix your stars in the body of your shells with pieces of cardboard between the stars, the stars must be fixed, hard to move them.

- I put the break charge separated from the stars with tissue paper or kitchen paper in the center. The forces of the shoot from the mortar and the spining of the shell in the air move the charge to the sides of the shells this cause very bad simetry.

I hope I have explained well sorry for my bad english

[greenlight]

Thanks everyone for the answers.

I will make some more 3 inch cylinders using the tips I have been given and see if I can get some decent breaks going.

 

I am about to make another batch of granulated black powder and I will use it for a centre canulle in tissue paper in the new shells with a layer of 7:1 rice hulls between it and the stars to conserve the granulat3d powder.

[Mumbles]

If you fill the space between the stars with polverone, like you should if building the shells properly, there's really no issue with burst migration. I still use a tissue paper liner, but that is more out of habit and for if I ever need to disassemble the shell.

[Wiley]

Building on what Carbon said, just place your canulle in the case, then jumble fill cut stars around it. Add some stars, then polverone. Tamp the fill with a wooden dowel, bounce the case on the workbench, and pat the outside of the case with your hands. The idea is to fill the spaces between the stars with the smaller polverone.

 

When the case is full, fill the canulle with granulated black powder, then withdraw it with a slight jiggling/twisting motion. Install your fused disk, close the case, and spike with string soaked with wheat paste.

 

Then again, there are many other ways to get a nice break from such a shell.

[greenlight]

Thanks mumbles and Wiley, I will be using a canulle of hot granulated BP and the spaces between the stars and casing will be filled with polverone for the next shells.

[greenlight]

I made another 3 inch D1 cylinder shell and this time used polverone around the stars, a middle canulle of granulated BP and 7:1 rice hulls around that. There was no loose material and all the gaps were filled.

 

This one worked out a lot better with a much more round full break and I am quite happy with it compared to before. I used additional lift charge to get them a bit higher too.

I don't have a youtube account so had to upload the file for download (don't know how to do it any other way).

Edited October 18, 2017 by greenlight

[Wiley]

That looks like a good improvement.

 

Were these pressed stars, stacked around the periphery of the case like bricks? If so, they ought to be packed in with polverone or bentonite kitty litter in the little triangular spaces. When finished "setting" the wall of comets with either of those fillers, you should be able to invert the case and shake it without any of the comets moving.

 

Now, place your canulle in the center. The space between the canulle and the comets can now be filled with small cut stars and polverone. If there is not sufficient room for cut stars, that space may be filled with polverone. The canulle is then filled with good powder and withdrawn.

 

You may also dispense with the canulle entirely and fill the whole central space left by the comets with black powder. This yields an especially strong break.

 

It's also worth noting that tremalon may easily be produced as a cut star. Doing so does not "ruin the effect" as some would have you believe. In fact, I find that when Ned Gorski's N1 is made with raw chemicals, it performs better as a cut star. When I want to use the same composition for pressing comets, I use the black powder base variant.

Edited October 18, 2017 by Wiley

[greenlight]

Thanks, they were cut stars for this shell but I just got a 3/8 inch star plate so the next will have coloured stars from the plate in it and they will be stacked in the pattern you specified.

Don't know whether 3/8 stars are too big for these 3" shells, maybe they would be better suited to a 4 inch.

 

I didn't know you could use bentonite for the outer triangular spaces I thought it had to be BP, interesting.

Edited October 18, 2017 by greenlight

[Mumbles]

You're probably going to be able to fit 14-17 per ring, and probably 6 layers high. If you want to stack 80-100 stars individually in a small shell, more power to you, but I'd personally just fill them like cut stars. They're probably a little big for a 3", but would be perfect for a 4". If you use a faster burning star or don't mind a little droop you'll be fine.

 

If you decide to stack them, it's not traditional, but I feel like I should be honest here. You can get away with some shortcuts in small shells. I also wouldn't worry about really packing them in. The space is going to be pretty small. It's more something that's necessary with inserts, comets, and in larger shells. Instead I'd use chipboard, or thin wood to shim them into tight rings. Fill in behind them with polverone if you'd like, but you'll need a pretty fine tool and a lot of patience to really pack everything in by hand.

[Wiley]

I agree, Mumbles. For 3" shells and even most 4", I would just jumble fill them with cut stars and polverone around a canulle. I would really only consider doing what I described for 5" and bigger shells. Then again, TR's headings are only 2.875" ID, or just a bigger than what you're working with. He loads quite a number of them with tweezers. It's just a matter of how much time you want to spend.

 

One effect that's easy to achieve with jumble-filled cut stars is a ring of dissimilar color/streamer. Simply fill the shell nice and level up to about half the length of the break. Then, place the dissimilar stars in a ring around the periphery of the case. Carry on jumble filling the rest of the case with the "normal" stars. If done carefully, you should see a nice contrasting ring every time.

[greenlight]

I filled mine with tweezers haha the only ones I have jumble filled are 2 inch shells.

 

I will make a batch of perc coloured 3/8 stars and try a 4 inch next.

Im guessing the larger in diameter you go the less need for a very powerful burst as there is more space for burst charge.

 

If you were to use pressed stars that are too large for a certain diameter shell (burn duration too long), is it possible to hand twist a small drill bit through the middle of each star when still wet to form a small central hole. The idea being a copy of propellant grain design which amounts to more surface area and a faster burn. This should, in theory, prevent drooping and increase burn brightness as well.

Only issue I can come up with at the moment is if a thick layer of prime is used it could cause fragmenting of the star from the central hole into two or more pieces similar to a crossette.

Has this been attempted already?

Edited October 19, 2017 by greenlight

[Wiley]

I know TR did something similar to get a blue formula to burn out at the same time as his other colors in a specific heading.

 

The 3/8" colored stars will be a little large for a 3", but that won't be a problem. They will, as Mumbles mentioned, be perfectly sized for a 4".

[Mumbles]

Granulated BP is the most common burst for cylinder shells. You don't really change that much. The strength of the burst is primarily controlled by the diameter of the cannule. I typically go on the larger side of things for a bit bigger breaking shells. There are some methods of boosting cylinder shells as well if it comes to that.

 

That was primarily for color breaks where the shell is just filled with stars and polverone. What you describe is nominally true for comet breaks or breaks in which the stars/inserts line the casing and the center is mostly empty. One common way to attenuate burst strength is to mix your hot black powder with polverone. Most of the time you design around this by filling in empty space with stars, but if that doesn't fit with the aesthetic of your shell this area can be filled with just polverone, or a mix of poverone and BP can be used to fill the whole cavity with no cannule.

 

Stacking stars with tweezers, hand drilling individual stars, this all sounds like a lot of work. The end result better be worth it. TR's shells definitely are.

[greenlight]

I wont be hand drilling any stars hopefully haha.

 

I just made 2 batches of colour perc stars and a batch of granulated BP for burst/lift for an attempt at a 4 inch cylinder shell.

 

I am making my granulated BP by mixing with 4% dextrin and wetting until I can rub it through a kitchen seive without the granules sticking together.

 

I saw a video on youtube where the BP is rubbed through a 4 or 6 mesh screen instead.

Is this a better eay to make the lift/burst with the larger size granules or is this more for larger size shells.

 

I have attached a picture of my current BP I have been filling 3 inch shells and lifting them with:

Edited October 23, 2017 by greenlight

[Bangkokpyro]

Your kitchen sieve B.P will work but 4 inch and larger cylinder shells are normally lifted and broken with granules in the range of -4 +12 mesh.

The 2FA should be used in center of the shell as burst (a 3/4 or 1 inch canulle is appropriate) and 2FA granulated Polverone used to fill the spaces between the cut stars to pack the shells contents tightly.

 

Your kitchen sieved B.P would be more appropriate for use in small insert shells.

 

2FA is adequate for lifting both 3 and 4 inch cylinder shells, finer granulations tend to slam the shell out of the gun too hard.

 

As for drilling holes in stars. Sounds like a lot of work nothing not to mention potentially causing the star to ignite. Better to stick to traditional building methods to achieve the effect you are after.

 

Get a copy of the Fulcanelli articles in Pyrotechnica for a good guide to building cylinder shells.

[greenlight]

Thankyou bankok pyro, seems like its time to start making 2FA for lift and burst now and keep the other BP for small items.

 

I wasnt actually planning to drill holes I was just asking if it is a viable idea if burn rates are too slow.

 

I will look for a copy, thanks

[greenlight]

I completed a 4 inch shell yesterday and finally got a mortar ready. I had to use a a cardboard tube that needed to be reinforced so that took longer as well.

 

I used 3/8 inch purple and lemon yellow stars with the yellows in a cross pattern around the length of the shell and the purple in between but the yellow well and truely masked the purple with the brightness. They also burned for longer as well.

The delay was a little too long as well, the shell started to come back down slightly before the delay burned through.

This is my first time using coloured stars though.

 

Burst was 2FA blackpowder in a 1.25 inch canulle and the spaces around the stars were packed with polverone meal and kitchen seive BP.

Edited November 7, 2017 by greenlight

[Wiley]

That looks like a pretty burst from the picture. Nice!

 

I just have a couple notes/suggestions:

The canulle stays in place until the shell is completely filled. The canulle is then filled with black powder and removed with a slight jiggling/twisting motion. Copper or thin-walled aluminum tubing make good canulles.

 

I like to wrap the canulle with 2 turns of tissue paper as Paul Moulder shows in his videos. Doing so eases the process of removing the canulle.

 

Are you rolling your casings wet? If not, there is no real reason to cut the ends of the case into "ears." Simply pleat the paper down onto the end disk.

 

If you are rolling a wet case, this cutting is best done after installing an end disk. Roll the case, slip it partly off of the former, install your inner end disk, and cut the overhanging paper into "ears" with a razor blade. Paste the ears down and install another disk on top of them. Do the same on the other end after filling the case.

 

I don't build in the Maltese style, so I always roll a dry case and pleat it down a turn at a time. However, Paul Moulder has some nice videos detailing the Maltese process, including making a wet rolled case.

 

Link to his channel.

 

https://m.youtube.com/channel/UCsfbkoc1N14UC3MokDwEyyw

Edited November 8, 2017 by Wiley

[greenlight]

I have been using a thin sheet of tissue paper as the canulle but I am still yet to go buy an assortment of different size metal pipes to use as formers for them.

 

I have been making wet cases with PVA/water solution and drying for a couple days then using them.

I will cut the ears after putting the end disk in next time.

Thanks for the tips.