Richtee Posted April 17, 2008 Posted April 17, 2008 The shell is either going up(in one piece or not), or the mortar is going outward. Seems to contradict "Every action has an equal and opposite reaction" considering the energy expended to light the fuse... ;{)
hst45 Posted April 18, 2008 Author Posted April 18, 2008 Sorry that I didn't elaborate on the construction, etc. I just posted the video as a "shell blows mortar all to hell, let's all laugh at hst" video, not as the far more useful analysis of what actually went wrong. Since I knew when I had to force-fit the shell I had made it too tight, I assumed the worst, so I wasn't surprised when it blew, and I really didn't give it much thought after that, but in retrospect it seems a "good" failure, since I learned something from it, and hopefully others have as well.
FrankRizzo Posted April 18, 2008 Posted April 18, 2008 EDIT: I posted the above last night, and since then I had a chance to think about why you asked. If I hear you right, you saying that the first flash might be just the quickmatch, and that in forcing the shell into the tube I crimped the quickmatch so it didn't reach the lift, but did make it to the timefuse on the top of the shell. That would actually make good sense, as it explains why the LIFT didn't blow the tube before the break charge. Sorry it took me so long to figure out what you were telling me. Thanks.Yep, that's exactly what I was referring to. The section of quickmatch that extends from the timefuse down along the side of the shell into the lift is properly called a passfire. Some guys simply cut a hole in the quickmatch tube near the timefuse to communicate fire, then continue to run it down to the lift charge. Others secure the end of the quickmatch directly to the cross-match on the timefuse, and then use another short section of quickmatch attached also to the timefuse and run along the shell to the lift. The second method is a bit more reliable and has the effect of a huge amount of fire at the timefuse ensuring ignition.
TheSidewinder Posted April 18, 2008 Posted April 18, 2008 I'm one who uses two seperate pieces of QM. I also use genuine Thermalite for my cross-matching. Makes a big difference, imho. I loop the exposed piece of the leader around the timefuse UNDER the cross-match, then wrap the exposed piece of the passfire around the timefuse OVER the cross-match. Then I carefully bend one side of the Thermalite around the QM (one side up, the other side down). Put the final protective wrap of Kraft on and cinch it down close to the timefuse. As Frank said, that produces a relatively HUGE amount of fire right where it's needed most. I haven't built THAT many shells, but I have yet to experience a lift or break failure. (How it looks AFTER the break is another matter, lol.) I attribute it to the above method and, notably, using Thermalite for my cross-matching. I've heard a few people say they have had bad luck with Thermalite, but they didn't prepare it like I do: Strip off EVERY last bit of that blasted fiber-type outer wrap that it has, AND remove 2 of the 5 wrapping wires which are under the outer wrap. That reminds me.... I have a partially-written tutorial on this laying abotu somewhere, with detailed pics, that I hope to have finished and posted before I die. I'll add that to my list of things to do.
Mumbles Posted April 18, 2008 Posted April 18, 2008 I crossmatch the time fuse as normal. The leader is split and a notch taken out of it. I physically slide the crossmatch into the slit, and tape it down securely. Strapping tape over the fuse, and behind and in front of the fuse as well. That way the tape bears all the force of gravity, when lowering it into the mortar, and the passfire isn't torn off. This combined with the bucket formed when the final dry wrap is added ensures a large amount of fire around for ignition. Never had a shell fail to light. Well, never had a can shell fail to light. Ball shells I have had 2. One had glue over the surface of the visco, and the other I don't know. I think the fuse was bad actually.
marks265 Posted May 26, 2008 Posted May 26, 2008 I made a 25 shot 3" HDPE cake it was loaded with mines and salutes. I was well away from this when it was firing and things got a little hot! Everything seemed to fire OK when looking upwards. But it came to clean up time and I was al ittle surprised when I walked up on battered assembly with 8 or so tubes scattered about. I think the mines were loaded a little heavy. 100 grams of 1/4" stars with 30 grams of lift. The tube is upside down as shown so the tape hanging on the tube denotes the top of mortar. http://www.apcforum.net/files/DSC00146.jpg http://www.apcforum.net/files/DSC00153.jpg These were the last 6" shells I made. The look pretty but broke like crap. Still have more things up my sleeve to try though! http://www.apcforum.net/files/DSC00148.jpg
Sambo Posted May 27, 2008 Posted May 27, 2008 Wow, i've never seen a mortar shreaded that much before, now thats what you call f**ked. That looks like one of your salutes blew in the tube, rather than a mine. Nice looking shells there, the pasting looks really good, have you figured out why you got a bad break from them yet?
Mumbles Posted May 27, 2008 Posted May 27, 2008 I agree. I've only seen salutes shred mortars like that. Well salutes and flitter stars that are pulverized from the lift. Some flitter stars are little more than bound flash powder. If it was an overloaded mine, I would have expected the Plug to give way, or a single tear out the side to make it look like a canoe. That looks like a mighty powerful blast.
marks265 Posted May 28, 2008 Posted May 28, 2008 I could easily buy the salute idea it's just that I did not notice a loud report at ground level. I felt the flame from lift ignited entire mine contents and gave the result seen. I was not in sight of it when fired nor was I able to account for all 10 salutes getting into the sky. So I'll never really know for sure. As for bad breaks, Is it possible to have too strong of a shell? I used 4:1 KP on rice hulls and 2 heaping teaspoons of whistle and only have noticed a slightly better break than black powder on hulls. I was actually thinking of adding 10 grams of flash with KP burst and try to prove or disprove my thoughts. Because I don't know what the hell I'm doing yet it is hard to say how many pasted layers there theoritically are with my method used. All I can say it is a pretty tight fit to the mortar. Infact I had to bury 5 mortars and then switch 2 of them because they were too out of round to fit! My second guess is that I am doing something wrong when pasting around the poles and actually have a weak shell. Which is probably more likely than the first guess.
Mumbles Posted May 28, 2008 Posted May 28, 2008 It's definately possible to over break a shell. The big give away is a huge break, but only a fraction of the stars lighting. It's possible to have a good break, but poor priming. Too little pasting is evident by a small break, or a poor pattern. The weak breaks I've made have more of an appearance of the stars just dumping out. I can usually tell by the sound. pm me, and I can send you an example of poor priming. Probably has a weak break too. Priming was definitely an issue though. I don't personally paste over the poles so I can't exactly comment on that. I did notice your shells had a definite pole shape. It's not bad necessarily, but some say it tends to give uneven breaks due to uneven layers. I started with my pasting method early on, so I didn't have much experience with poles. I'd be happy to explain more via pm.
oskarchem Posted June 26, 2008 Posted June 26, 2008 Here's another addition from me: I was firing a 80mm x 300mm shell. I had Win 20 stars and 4 1-3/4 flash inserts. Anyway the whole thing was underlifted and it got out of the mortar went into the sky, then came back to earth and landed behind my pool. This was on my father's birthday, anyway I knew this was gonna be loud so I hit the ground and my parents instinctivly did too. All of the other guests just stood there. Evryone was about 20m from the shell. Anyway, the spolette burns out and KABOOM, the loudes't report I have heard in my life, all of the inserts blew together. No one got injured well exept 2 flowerpots that were in poroximity of the shell +- 5m got shattered and I made a crater in my lawn (not that I am proud of it). So now I put alot of lift into my shells (well 1/9th of the weight) I find that it's better to make it blow higher than lower. Stay Safe
Mumbles Posted June 26, 2008 Posted June 26, 2008 Why would you even think about firing a shell with large-ish salutes in it that close to a crowd, much less at all with lift you were unsure about?
oskarchem Posted June 27, 2008 Posted June 27, 2008 The mortar was further from the crowd than the 20m it was like 40-50, but it arced and fell close to it. I was sure about the lift I did calculate 1/10 af the weight. It fit snuggly into the mortar and all of that.
justanotherpyro Posted July 4, 2008 Posted July 4, 2008 This one counts as a failure. I tried a modified red comp which just completely failed me. Its a 6" with the modified red and a TT cross. It still came out cool and was awesome but only a few of the red stars lit and they looked orange. http://www.apcforum.net/files/JAP6inchTTcross.wmv
psyco_1322 Posted July 6, 2008 Posted July 6, 2008 Well its the opposite but the good thing is my lampare for the 4th came out beautiful. Didnt kill anyone, and the mortar got its above ground stress test.
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