Ric,
This was a new system to me also. The Det. cord pictured in the water have a powder compound in them as does the cord between the det. cord. The det. cord was larger in diameter and the explosive inside was suspended in some type of caulk (?) and waterproof. The forester doing the instruction said it didn't hurt to put it in the water and evidently didn't matter as it took a couple hours for them to set up the large dam. The explosives described above were in plastic bottles that had a recessed grooves, the full length of the bottles, on opposite sides, sized correctly for the det. cord to just lay tight along the length of the bottles, in the grooves. Around the top and bottom of the bottles were plastic bands to hold the det. cord tight to the bottle. To rig the bottles you just push the det. cord into the groove, under the plastic band, the full length of the bottle and under the top plastic band, then about 6" longer than the bottle and then take that extra length of det. cord and under the plastic band on the opposite side, to keep it tight to the bottle and secure the loose end. They put two charges/ bottles in each hole bored in the dam so just aligned the grooves on the bottles, ran the det. cord the length of both bottles , in the grooves and under the plastic bands and tucked the extra length under the plastic band and into the groove on the opposite side. Then they used electrical tape to tape the bottles together at the joint and to a stick to push them to the bottom of each hole, then back filled the holes with loose debris. They cut the det. cord with what looked like a pair of hand pruning shears.
If you look close at the pictures , you will see on the ground, between the guys standing, there is a coil of cord. In that coil is a plastic coupling, sort of like a wire connector, when snapped together holds the det. cord to the lead cord. The det. cord coupling has a igniter (small metal tube with ignition compound/ explosive in it, and has a tailpiece of det. cord about 6' long. The main trunk line det. cord lays along side of the igniter, in the coupling, for approximately two inches, inside the plastic coupler. Then the plastic coupler is closed. The length of det. cord that is then run from the plastic coupling to the farthest charge and is called a main trunk line(His terminology) . Then all the det. cords coming from each charge are coupled to the trunk line. To determine actual sequence of detonation can be determined by length of det. cord, or in short, closest to igniter first to explode.
After the rigging was all done, a smaller diameter "lead" line, on a reel, was spooled out away from the dam for approximately 250'. This "lead" line was just the right size to fit into the tail end piece of det. cord coming from the igniter. I believe he also taped that, but can't recall for sure. This lead line has a small nipple cap on it and the instructor stated this is where most miss fires result from. He cut off about a foot of the lead line before installing it. The lead line is just a hollow plastic line with a white powdered priming compound in it. He stated if it gets wet before detonation the line can draw water and the priming compound can get wet. He hung it in a bush off the ground while we cleared the area.
Once we were clear of the dam, the lead line is installed in a small device that looks like a letter T with a short leg , and collar on one end that holds a die, that looks roughly like a shell holder. This shell holder is the appropriate size to accept a 409 size primer, and like a shell holder has a hole all the way through it, and sized to accept the lead line. The primer is inserted into the shell holder, inserted back into the collar. The actual striker retainer looks like a drift pin with notch cut in the center and retains the T shaped firing pin. The end of the drift pin is a retained coil spring that acts on one end of the spring. The firing pin is cocked and held in that position when placed in the notch. There is a hole through the drift pin for a hitch pin clip to work as a safety device, or block the firing pin. There is an appropriate sized hole on the side of the shell holder to allow the lead line to be ran through it in a generous loop, then the end placed in the inline hole of the shell holder. In short, it looks like a Zip Gun with a shell holder on one end with a yellow tube coming off it!
They advise yelling fire in the hole or blowing beaver dam etc, then listening for a reply. After the second warning ,the hitch pin clip is removed. A third warning then the short leg of the T is moved out of the notch and the spring sends the firing pin forward striking the primer. The priming compound ignites the igniter, which ignites the det. cord to charges. I watched his thumb and there was a very short lag time from strike of primer to boom.
They wound up the lead line and there weren't any traces of det. cord remaining. That kind of surprised me as I've pulled lots of the old style lines out of dams over the years.