Right, NO pipe bombs. This is kind of a variant on "rocket candy", so no explosion but thrust was a concern. I tested this same mix in cardboard tubes previously, so I knew in general what type of reaction to expect but wasn't sure how much thrust there'd be with it venting out of a 3/8" hole (hence the milk crate and the rock in the pic). The propane can itself has a pressure relief valve too, but I wasn't relying on it.
Anyway, not a bad result, lots of smoke, but still seems kind of thin/wispy. Breezy day today so it dispersed fairly quickly too. The burn time was about 60 seconds, full burning. Really thought I had a dud, I used about a foot of fuse so it was curled up in the cylinder in the mix to give it a better chance of igniting - but it took about 20 seconds after lighting the fuse for it to start smoking. Once it did start smoking, the next 10 seconds or so was just some very thin smoke trickling out. Then WHOOSSSSHHHH and the full burn started. In full burn mode it was expelling gas under a lot of pressure. See the melted milk crate, and the cylinder afterwards - definitely a fire hazard so be careful but the cylinder didn't move or even fall over and it was only in the sand about an inch or so.
It's a 3:2 mixture of potassium nitrate and Karo syrup (main ingredient, corn syrup). The cylinder easily held 300 grams of KNO3 and 200 grams (5.54 fluid ounces) of Karo, or slightly over 1 lb total. Creating it was pretty simple once I got the KNO3 crushed in the grinder, and heated the Karo syrup slightly so it poured easy. I put the Karo in first, then poured the KNO3 in second - both using the funnel. Stirred with a wooden shish kabob skewer through the hole in the cylinder for a good 20 minutes. I tried using both granulated sugar and powdered sugar (w/o heating the mixture) but didn't get very good results. The liquid Karo works much better, and doesn't require cooking the mixture.
Total time: about 40 minutes, but pretty sure that'd come down with practice.
Material cost: about $4 each ($5 for enough KNO3 to make 2 smoke bombs, and $3 for Karo enough for 3). Supplies and propane can extra.
Worth it IMO? It's an arrow in the quiver of preparedness I suppose, knowing the basics of how to do something is great but not everything goes smoothly in the real world. The first failure I had was two-fold, too much mix to fit in the cylinder and the marinade injector/syringe idea (see the first pic) didn't work at all as I thought it would. Sticky, gooey mess basically and was loosing so much to overflow I couldn't be sure of the ratio anymore. Had it been an actual SHTF situation, I'd have wasted a lot of time and materials.
I think I'll make up some more, maybe try adding some Ghost Pepper extract to the mixture, see about adding some dye for color, and try igniting it with an electronic match (have had an ematch kit for a couple years but never built any). I'm thinking the most likely way I'd use them would be to pre-position them if the SHTF, and then be able to set them off remotely if needed. Maybe even automatically from a motion sensor in a real EOTWAWKI situation.
Sorry for the huge pics, image hosting site giving me some issues and couldn't easily re-size them.
Everything marked, everything 'membered. You wait, you'll see.