laserkoi Posted December 26, 2012 Posted December 26, 2012 hi all . having just tested my first 4" shell . its flight path had a wide ark ( ie it was comming back down before it burst ) shell weight was 420grams with out the lift cup . it had a 3sec 1/4 " time fuse assembley, clearance in fireing tube was around 1/8 " lifted with 41 grams of my bp . now was the problem a.) time fuse too long ? b.) was my bp not quite up to the job ? build photos are on my profile here http://www.amateurpyro.com/forums/gallery/album/157-first-attempt-at-making-4-shells/ look forward to your input .thanks for you time
ivars21 Posted December 26, 2012 Posted December 26, 2012 If I have to guess, I would say that your BP is not hot enough. I usually use 3.5sec delay for my 4" and they blow up at the right time. And usually clearance in my mortars is around 5mm
dagabu Posted December 26, 2012 Posted December 26, 2012 I will second Ivars comment, 41g should heave the shell to the correct height. -dag
dynomike1 Posted December 26, 2012 Posted December 26, 2012 (edited) I use 2oz or 56 & 3/4g. with my BP, @ 3.5sec. delay looks like it breaks right in there. Edited December 26, 2012 by dynomike1
Arthur Posted December 26, 2012 Posted December 26, 2012 (edited) Well it sounds as if the lift is weak, To get round the issue, use 10% more lift or make the shell fit the tube better. However getting really good results usually comes with really good BP. If your shell breaks too low the stars may come back to the ground and bite you back. There is a basic test to launch a cricket ball from a mortar and time it's flight time. Better BP gives longer flight for the same mass of BP. A cricket ball may be a rarity for you but a baseball from the right size mortar will have the same test value. IIRC a cricket ball can fly for 12 seconds from a vertical mortar. -Just be very careful that there is space to test as the ball will need a place to land in -no cars houses etc! Edited December 26, 2012 by Arthur
laserkoi Posted December 27, 2012 Author Posted December 27, 2012 (edited) thanks for all the reply .the shell reached its peak trajectory at just over 2 seconds , it was short only by 3/4 sec . i will check my bp . did the 1 gram test open burn on paper . just left a scorch mark no residue .i have plenty of space were i fire ( on private land ) the nearest neighbour is 1/4 mile away .i will launch a cricket ball at the weekend and time its flight . hope you all have a good new year , hope its a nice night for some pyro fun . Edited December 27, 2012 by laserkoi
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