jrin0630 Posted July 5, 2009 Posted July 5, 2009 I shot my first 3" shell yesterday and it flower potted. It was a 165G 3" ball shell shot out of a 3" HDPE mortar with 15G of BP lift. The time fuse was a 3" piece of Chinese green visco. I had about 2/3 of the take fire end wrapped with masking tape for some extra protection. When it went off there was virtually no delay between the lift and the burst charge. It all went off in the mortar at once and flower potted. Anyone have any thoughts on possible causes???
50AE Posted July 5, 2009 Posted July 5, 2009 I think it may be a fire leak near the fuse. How do you glue the fuse in the hole ? I suggest using hot glue on the outer and inner side of the hemi and putting some on the area where the masking tape starts.
jrin0630 Posted July 5, 2009 Author Posted July 5, 2009 I think it may be a fire leak near the fuse. How do you glue the fuse in the hole ? I suggest using hot glue on the outer and inner side of the hemi and putting some on the area where the masking tape starts. That's exactly how I glued the fuse. Hot glue in and out of the hemi around the tape. As I've been thinking about this, I wonder if this is a possible cause. The take fire end of the time fuse was wrapped 2/3 with tape (several turns). Could it be that the gasses from the lift traveled up through the tape and into the shell. In effect creating a tunnel of fire right into the burst. I'm thinking of using only enough tape for the hot glue and leaving the rest of the time fuse exposed, in the lift cup. Not sure if this theory is valid.
jrin0630 Posted July 5, 2009 Author Posted July 5, 2009 Was the shell pasted?? Yes. 12 layers of 30lb Kraft.
Swede Posted July 5, 2009 Posted July 5, 2009 (edited) That's exactly how I glued the fuse. Hot glue in and out of the hemi around the tape. As I've been thinking about this, I wonder if this is a possible cause. The take fire end of the time fuse was wrapped 2/3 with tape (several turns). Could it be that the gasses from the lift traveled up through the tape and into the shell. In effect creating a tunnel of fire right into the burst. I'm thinking of using only enough tape for the hot glue and leaving the rest of the time fuse exposed, in the lift cup. Not sure if this theory is valid. That's actually not a bad theory. The lift ignites, creating a pressure spike and a huge differential between the interior of the shell and the outside. The hot BP gasses will find the tiniest crack or crevice, delivering its fire to the interior of the shell, making your flowerpot. I use visco on festival balls and tiny shells, but even 2" I prefer real time fuse. Can you not get any? When you think of the work and materials that go into a decent larger shell, it's worth it. Plus, visco burn rate varies even in the same roll, and you won't have the precision that you want and need. One way to turn visco into respectable time fuse is to use heat shrink tube. If your visco is 1" long, cut a piece of heat shrink tube 7/8" or so, and install it so the passfire end of the fuse is even with the heat shrink, and you'll have 1/8" of fuse outside the shell to take fire from the lift after priming w/ NC and maybe BP. The heat shrink is adequate to contain the fire until it reaches the end. Edit: Obviously use great caution when you shrink the tube, and do it well away from any comps. I haven't had it happen yet, but it's certainly possible. Edited July 5, 2009 by Swede
50AE Posted July 5, 2009 Posted July 5, 2009 (edited) But I also said to put glue between the tape and the fuse, to seal it. As Swede said, fire could easily pass through.I suggest using real time fuse, or you can't find/afford any, make yourself spolettes. Edited July 5, 2009 by 50AE
Mumbles Posted July 5, 2009 Posted July 5, 2009 I've occasionally had problems with timing on visco. I don't know how well the masking tape adheres to the lacquered finish, and I think may occasionally make air pockets as it pulls away. I've never had a flower pot, but a few that were close to muzzle breaks, going off less than 50 feet in the air, very much still on the way up. The only way I figured this out is that in testing of the fuse I had one "quickmatch" up a bit. The most reliable method I found was to wrap the fuse with a few layers of Al foil, covered by paper, everything glued down with elmers glue.
firetech Posted July 5, 2009 Posted July 5, 2009 I use Aluminum foil tape. Not only does it have a great adhesive backing but its fireproof and fairly rigid.
jrin0630 Posted July 5, 2009 Author Posted July 5, 2009 I use Aluminum foil tape. Not only does it have a great adhesive backing but its fireproof and fairly rigid. Thanks for the feedback. At the end of the day, I think the masking tape was the cause of the premature ignition. I like the heat shrink idea and the aluminum foil tape idea. I'll try em both.
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