Shell performance questions

[cogbarry]

Hi all,

I'm a bit of a newby - started doing this last summer. The link below is a 3" shell filled with the red rubber stars from skylighter. Burst was BP coated hulls, the BP made from skylighters air float charcoal (commercial FFG is used for lift). Shell contructed from cardboard hemis and pasted with craft/paste until it fit the 3" gun well. I had read that bursting the shell in the center is not so critical for smaller shells but it seems that only half the stars in this shell lit and I wonder if this could be the problem. I used 1/4 chinese time fuse which does not reach the center of the shell. I plan to build my next shells with a passfire tube. Also, I added about .5 grams of flash booster. Could it be that I broke this shell too fast/hard and half the stars never saw fire? I plan to eleminate the booster for the next shells, it looks like the shell burst hard and I think round. Any comments would be appreciated.

 

http://www.youtube.c...h?v=2U8ef8sSQjI

[ExplosiveCoek]

What kind of priming did you use? Add some more hot priming on these (metal based) stars to get everything going smoothly. Finish the hot prime with some blackpowder.

[marks265]

I agree with what Expl... says. Also I like to stay away from flash boosters because of the flash of light to begin with. A black powder using potassium perchlorate as the oxidizer on hulls will work effectively enough for starting out. It also looks like the top half of the shell lit and the bottom did not. Did you use a lot of tissue paper in that shell?

 

Mark

[cogbarry]

What kind of priming did you use? Add some more hot priming on these (metal based) stars to get everything going smoothly. Finish the hot prime with some blackpowder.

 

The stars are parlon based...

http://www.skylighter.com/how_to_make_fireworks/Red_Rubber-Stars.asp

 

They do have about 3 layers of prime on them, hot prime, step, then the final. Followed the skylighter directions to the "T". You're like the 3rd person that seemed to suspect a priming issue. I'm a bit confused though. These stars lit fine for me when I tested them from a two inch plastic shell (broken a bit soft). Also, the stars in the shell were all the same and half of them lit fine. Thanks for the response!

[cogbarry]

I agree with what Expl... says. Also I like to stay away from flash boosters because of the flash of light to begin with. A black powder using potassium perchlorate as the oxidizer on hulls will work effectively enough for starting out. It also looks like the top half of the shell lit and the bottom did not. Did you use a lot of tissue paper in that shell?

 

Mark

 

Thanks! I ordered the chems I need to make whistle mix. Also, I am making my first batch of home made pine charcoal for the burst. Skylighter's hardwood charcoal is a bit slow. Do you have the recipe for the potassium perchlorate oxidized mix? Do I simply replace the potassium nitrate in the standard 75/15/10 BP?

 

Interesting question regarding the tissue paper. I used one sheet between stars and burst but used one extra on the top half to keep everything in place while snapping hemis together. I had asked someone if this could cause an issue, then felt silly for asking it. I didn't think the tissue could stand up long enough to create a barrier. However, it would certainly explain the symptoms. Has this been know to cause issues? Thanks for your response!

[ExplosiveCoek]

Some say it does make a difference, I do the same thing like you do.. And have never experienced any difference, al ways a good break .

 

The point is why I'm thinking of a priming issue: The shell broke alright.. but a little bit soft, so all your stars should have ignited quite easily.. But they didn't .

 

What do you mean by 'final' prime, blackpowder?

 

If you watch closely, you can see a 'star' on the left side of your break.. Which is burning but failing to ignite the red. Also looks like you've used quite some coarse metal (in the center of the shell).

[marks265]

Thanks! I ordered the chems I need to make whistle mix. Also, I am making my first batch of home made pine charcoal for the burst. Skylighter's hardwood charcoal is a bit slow. Do you have the recipe for the potassium perchlorate oxidized mix? Do I simply replace the potassium nitrate in the standard 75/15/10 BP?

 

Interesting question regarding the tissue paper. I used one sheet between stars and burst but used one extra on the top half to keep everything in place while snapping hemis together. I had asked someone if this could cause an issue, then felt silly for asking it. I didn't think the tissue could stand up long enough to create a barrier. However, it would certainly explain the symptoms. Has this been know to cause issues? Thanks for your response!

 

That is correct swap 1:1 nitrate/perchlorate and don't forget to add an additional 5% dextrin for binder (75/15/10+5). One or two layers of tissue is OK between halves. A boat load of tissue is not. You're going in the right direction with your charcoal as well. For things such as lift and burst a very reactive charcoal is best.

 

When you say three layers of prime I hope it adds up to 1-2mm of prime. Cut stars are easier to light than round stars so I venture to say your layers were not that thick?

 

Mark

[cogbarry]

Some say it does make a difference, I do the same thing like you do.. And have never experienced any difference, al ways a good break .

 

The point is why I'm thinking of a priming issue: The shell broke alright.. but a little bit soft, so all your stars should have ignited quite easily.. But they didn't .

 

What do you mean by 'final' prime, blackpowder?

 

If you watch closely, you can see a 'star' on the left side of your break.. Which is burning but failing to ignite the red. Also looks like you've used quite some coarse metal (in the center of the shell).

 

I sure do appreciate all the feedback I'm getting here. This forum rocks! Hope I can help others at some point. I mixed two types of prime as follows:

 

Hot Igniter Star Prime

Chemical Percent Factor 3 oz 85 g Potassium perchlorate 71% 0.71 2.15 oz 60.3 g Charcoal, airfloat 14% 0.14 0.4 oz 11.9 g Red gum 9% 0.09 0.25 oz 7.7 g Magnalium 6% 0.06 0.2 oz 5.1 g

 

Black Powder Parlon-Star Prime

Chemical Percent Factor 3 oz 85 g Potassium nitrate 67% 0.67 2 oz 56.9 g Charcoal, airfloat 14% 0.14 0.45 oz 11.9 g Sulfur 9% 0.09 0.25 oz 7.6 g Magnalium 5% 0.05 0.15 oz 4.3 g Red gum 5% 0.05 0.15 oz 4.3 g

 

The middle layer is just the two primes mixed as sort of a step prime I guess you could say. I pretty much followed the directions from http://www.skylighter.com/how_to_make_fireworks/Red_Rubber-Stars.asp.

 

I suspect most of the visibly burning center of the burst pattern is burst charge. This is the BP coated rice hulls. The magal I used from skylighter came mixed with turnings. I screened this through a fine screen but after I had started mixing the comp, I noticed there were still some courser flakes that got thru. Maybe this is the source of the course metal indications you are seeing? I'm still pretty green, learning not to rush things too much but there ya go - I should have been more careful there. I had hoped it wouldn't do much other that give me an extra unintended glitter effect.

 

The skylighter hardwood BP is pretty slow and I don't use it for lift. I don't trust it enough for that so I'm using commercial FFG. I'm bent on getting away from this, I'm about to make my first batch of BP using my own charcoal. In any case, the more I'm hearing folks tell me the burst is soft, the more I think I really need to fix the burst charge. Seems the shell did burst round but one side saw a lot more heat/fire. Also, no one has mentioned the lack of igniting the shell in center. I suspect the time fuse method without a spollete or passfire tube is commonly used in 3" shells.

[cogbarry]

I

That is correct swap 1:1 nitrate/perchlorate and don't forget to add an additional 5% dextrin for binder (75/15/10+5). One or two layers of tissue is OK between halves. A boat load of tissue is not. You're going in the right direction with your charcoal as well. For things such as lift and burst a very reactive charcoal is best.

 

When you say three layers of prime I hope it adds up to 1-2mm of prime. Cut stars are easier to light than round stars so I venture to say your layers were not that thick?

 

Mark

 

Thanks Mark,

The stars have some prime on them (dusted on the patty) before they are pushed thru the screen to form them. Then, I roll them and they grow from 1/4 inch to 3/8 or more. I had some trouble rolling the stars as the container I was using wasn't quite large enough. Had to split them up and do it in two iterations. I have since purchased a better rolling bucket. In any case, it seems that almost exactly half of the shell failed while the other half lit. Seems there must be another factor, even if I did have a lack of prime?

 

I will try all of the ideas I have got from the feedback here or some combination of them. I've learned in the IT world (where I work) not to change too many things at once, you may not know what you fixed or broke. I'll pay more attention while I'm rolling on the prime. I also know that I need to work on a better burst and/or booster.

[Peret]

it seems that almost exactly half of the shell failed while the other half lit. Seems there must be another factor, even if I did have a lack of prime?

I've had similar failures. I was able to recover the hemispheres later and found them unbroken, and one half wasn't even scorched. I conclude they broke apart at the seam early in the break and one half, plus its stars, blew off ahead of the flame front and didn't light. These were plastic shells made in the afternoon and shot the same evening, so the glue didn't have time to set properly.

[cogbarry]

t

I've had similar failures. I was able to recover the hemispheres later and found them unbroken, and one half wasn't even scorched. I conclude they broke apart at the seam early in the break and one half, plus its stars, blew off ahead of the flame front and didn't light. These were plastic shells made in the afternoon and shot the same evening, so the glue didn't have time to set properly.

 

Thanks for that. In my case the shell was pretty well pasted and solid. However, from everyone's observations and then my own repeated views of the vid (slow motion,etc) I am convinced the shell was under broke. I had thought the opposite may have occurred but after the feedback here I started looking at other folks vids of similar shells. My break IS much softer. I have read about the importance of the shell construction (ability to contain) in combination with the right burst charge. One of my theories is that the shell contained the pressure but the burst was so weak that it built up pressure and burst the shell before all the stars got good (or at least even) fire. Any takers on that theory or am I still in the dark?

[Mumbles]

It's definitely not an impossible theory. It's hard to tell withough being there in person, but my opinion is on the priming as well. Piping a lot of fire into the shell definitely helps to ensure ignition. I know you don't want to experiment with two things at, but I'd change the burst AND pipe fire to the center of the shell. If you want to stick with one variable at a time, just tell yourself that the piping to the center is proper technique, not an experiment

 

It definitely sounds like you are on the right track, and will be making good shells in no time.

[dagabu]

I agree with you, I have had several weak shells that split instead of shatter. I found that strapping tape helps immensely in keeping the equator from just splitting and dumping the contents. Small shells (plastic especially) are pretty hard broken, they will often have a very sharp "crack" sound from the flash or whistle booster.

[cogbarry]

It's definitely not an impossible theory. It's hard to tell withough being there in person, but my opinion is on the priming as well. Piping a lot of fire into the shell definitely helps to ensure ignition. I know you don't want to experiment with two things at, but I'd change the burst AND pipe fire to the center of the shell. If you want to stick with one variable at a time, just tell yourself that the piping to the center is proper technique, not an experiment

 

It definitely sounds like you are on the right track, and will be making good shells in no time.

 

Actually, piping to the center IMHO (which doesn't mean dog doo yet) could only be an improvement and like you said, I would not consider that an experiment so much. I may not know if that was THE major factor but I think getting used to good habits can do nothing but help. It takes me a while to build one of these shells! Why torture yourself with shortcuts that you know may make a difference?

Regarding the priming, I can only try to be more attentive I guess and obviously it helps to have the right equipment on hand when rolling these in order to minimize error due to running around like a chicken with no head while these rubber based acetone solvent stars are drying. Haste makes waste right? Your comments are exactly what I was looking for in trying to get a feel for this!