DeepOvertone Posted March 28, 2009 Posted March 28, 2009 I've been busy working on my first shell. Its a 4"er. Anyway, I am curious how close to the ID of my mortar should my shell be? I measured my mortar and the ID is 3 15/16". My pasting method has been: 1" wide strips overlapped going from pole to pole then done again on the other two axises. This was done 4 times for a total of 12 wraps. But it may have counted for more since I was over lapping them a bit. I've been using 30# Kraft so it hasn't built up as fast as I would have liked. If I put the shell down the mortar and push it against one side, there is about a 1/4" gap. Should I paste one more set of three axises? That would bring the gap to about 1/8". What is the appropriate size for this thing? In my mind, when lowered down the throat of the mortar, it should be basically touching all the sides as it slides down with basically no effort. I want to give my lift all the chances it can to get that thing up there. I'm also worried about the amount of pasting I have on there all ready. I used 70/30 boosted bp on rice hulls. I don't want to have gone over board on the break and pasting, and blow my stars to kingdom come. The stars are 1/2" pumped D1 unprimed. Think all should go well? I'm hoping I didn't make a mistake by not priming them. As far as I can tell from all of my tests, they lit pretty much as easily as a primed star. Thanks for all of the advice, now and in the past! Posted picture is from my first pasting while it was still kinda wet. It looks allot better now!!
Arthur Posted March 28, 2009 Posted March 28, 2009 There is no unique answer! More pasting will make the case stronger so the burst may be harder. Also remember to leave room for the leader match. Each design you make will have it's own best dimensions. There is always a trade between parameters, the burst compound must break the case and light the contents. The lift will give an elevation depending on the shell OD and the mortar ID too much gap will mean a lower break but too little gap and there may be a jam up in the tube.
FREAKYDUTCHMEN Posted March 28, 2009 Posted March 28, 2009 More space between mortar and shell means more lift. There are too many variables in pyro to get an clear answer to your question. You'll need to do tests to get answer to these type of questions.
TheSidewinder Posted March 28, 2009 Posted March 28, 2009 I believe you have that backwards. MORE clearance means LESS lift.
Sambo Posted March 28, 2009 Posted March 28, 2009 (edited) Is your lift adequate? Have you tested it with a dummy shell/burn rate test? Most of my shells have similar clearance and they lift fine, so you should be ok as long as your bp is good. You could always add a bit extra lift, do you use 1/16 shell weight for lift powder or 1/10? I prefer 1/10 as my lift is not the fastest. Edited March 28, 2009 by Sambo
swervedriver Posted March 28, 2009 Posted March 28, 2009 I believe you have that backwards. MORE clearance means LESS lift. more clearance space = more lift charge, correct?
swervedriver Posted March 28, 2009 Posted March 28, 2009 The stars are 1/2" pumped D1 unprimed. Think all should go well? I'm hoping I didn't make a mistake by not priming them. As far as I can tell from all of my tests, they lit pretty much as easily as a primed star. Star gun test? my D1 stars blew blind without prime, but they are rolled, without benefit of pumped star edges.
Mumbles Posted March 28, 2009 Posted March 28, 2009 Yes, more clearance = more lift. I think you'll be fine with what you have. The leader and stuff will take up some room too. I always prime my stars, but many people can get by without priming glitters and streamers and stuff.
h0lx Posted March 29, 2009 Posted March 29, 2009 Be darn careful with that, your first shell and a 4 incher? Make sure you are far away. Be safe.
DeepOvertone Posted March 29, 2009 Author Posted March 29, 2009 Yeah I think my lift should be pretty good. Its commercial airfloat milled for quite a long time. I'm using the red gum method from the skylighter article. The BP is just powerful enough to make end burner rockets so it should work ok. I'm certainly going with 1/10 shell weight just to be sure. The tests i've done on my stars were in 1" mortars. Bottom fuse with a little BP down there, drop in about 5-6 stars and let her rip. Worked fine. I know this is not a perfect analog to what a shell break is like, but we shall see wont we? I should be letting it fly in a couple weeks. Got a bunch of other stuff I'm working on to finish before then. Stay Safe!
al93535 Posted March 29, 2009 Posted March 29, 2009 shell size to mortar size. Star gun tests are too test if the stars are igniting well. If your stars worked well in a star gun they will work well in a shell. That is of course if they break isn't extreme. I don't believe I ever primed any BP type star comps. Glitters, streamers or anything of that nature... How much did you boost the break? how many grams of flash?
TheSidewinder Posted March 29, 2009 Posted March 29, 2009 Whoops. Sorry, when you said: "More space between mortar and shell means more lift", I thought you meant "more clearance would result in the shell going higher" (more "lift" of the shell), rather than needing to USE more lift.
Swede Posted March 29, 2009 Posted March 29, 2009 That confused me too. The statement should read "More clearance requires additional lift powder." All else being equal, a tighter fit with a given amount of lift will send the shell higher. Interesting chart al93535... the summary seems to be pretty simple. A ratio of shell size to mortar ID should be between 0.85 to 0.90 or so for best results, and it seems to hold true throughout the entire range of sizes. Good post.
DeepOvertone Posted March 29, 2009 Author Posted March 29, 2009 Honestly I didn't weigh the flash I used to boost. I went by eye based on what I've seen everybody else do. I would say there is about a level teaspoon in there. Maybe a bit more. So a few grams??? I know that I should have weighed it so I could learn from my experiences. Oh well, I'll be more thorough next time. I will also have more pictures from star to finish. I got a new point and shoot camera. It was such a pain to break out my DSLR for these simple photos. I'm definitely going to do one more pasting to bring the size up a bit. Should be firing it in a couple weeks. My friend works for a local TV station doing on location video and he can borrow their video camera any time he wants, so I should have some really good video of it!! Hopefully it won't be a high quality video of how to fail.
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