Due to neighbor complaints (I could sort of understand their concerns when stuff kept falling off the walls) I’m reducing the target volume on the largest targets this year. I’m gluing part of an egg carton into the bottom of the 8“ target bodies prior to filling them with explosives.
I’ve measured the capacity and now the 8” targets have just about the same capacity as the 6” targets while still offering a larger shooting area. I can get all the old egg cartons I want at the recycling center but the time involved is almost painful. Including the cutting, fitting, and gluing it’s taking right at five minutes per target. Since I plan to have 60 of these size targets that means I’m going to be putting five hours of prep time just for these targets. Well I guess the consolation is that if I loose money on the event this year it will reduce my loss in terms of $/hour. Instead of earning -$1.00/hour I’ll earn -$0.98/hour or some such thing. That’s better–isn’t it?
For some of the background on this read my web pages on Reactive Targets–especially Project Nitro. The recipe given there is obsolete, but it will still help you understand some of what follows.
The last year the targets just didn’t detonate as well as they should have. We changed the containers we used for the targets, we ground the NH4NO3 much finer that ever before, we used a KitchenAidR mixer instead of hand mixing, and we put in a small amount of MnO2 as coloring to help us tell when it was thoroughly mixed. Too many variables and we discovered the problem just a week before the event. We suffered through the event and then last fall I bought some books on explosives and detonation mechanisms and have spent a lot of time reading and thinking about what is going on with our mixture. Some of my hypotheses were shot down after doing a few thought experiments. Some others died after some field experiments. My latest hypothesis is that when we grind the NH4NO3 it absorbed the liquid fuel (proprietary) and the KClO3 isn’t able to interact with the fuel as well during the detonation initiation phase. This might also explain why the mixture becomes more and more difficult to detonate as the targets age–the fuel is absorbed more and more into the NH4NO3 and it’s also possible it is evaporating through the container walls. Fortunately if this hypothesis is correct the fix is easy–add more fuel and perhaps seal the containers better. For maximum sensitivity the mix has always been very oxygen rich and I have wanted to add more fuel just to get more bang for the unit volume of target. If adding more fuel works out I’ll be pleased for more than one reason.
Most recently the ratio of NH4NO3 to fuel has been 24:1 by volume. This was based upon a density measurement from a long time ago with a different batch of NH4NO3 and I decided to measure the density again before doing these tests. Previously I had measured a specific density of 0.96. This time I came up with 0.875. Ouch! That could be making a difference too. Time to redo all our sensitivity tests. Tonight I finely ground four 500 mL batches of NH4NO3 and mixed in 20, 30, 45, and 60 mL of fuel in the respective batches. That gives me ratios of 25:1, 16.7:1, 11.1:1, and 8.3:1. I was amazed at how little of the fuel shows up in the 25:1 mix. It’s almost as if it doesn’t exist. I’m expecting that after letting it “soak” for a couple weeks even the 8.3:1 mix will look pretty “dry”. After the next IPSC match (February 6th) I’ll mix in 125 mL of KClO3 in each mixture and do the sensitivity tests while at the range. This year I’m going keep tweaking things until we get everything working right again.
It sounds sort of like an Unintended Consequences story line. From the website:
The year is 2018, seven years after the successful end of an American-led world war on terrorism, but the nation is now faced with an even more horrible prospect: a war against an enemy it can not defeat—itself. In the face of the gathering storm clouds of war, Jeremiah Kincaid, 59, the Republican Speaker of the House, struggles to mediate a growing firestorm of public debate over gun control. On the left is Alexander Webster, 49, the Democratic President, who halfway through his final term, decides to make the elimination of guns from America his legacy. On the right is Edward Morrissey, 61, the Republican Governor of Idaho, who bitterly opposes the President’s position.
Exacerbating the situation, militia seize a gun club built on Federal land in the Bitterroot Mountains of Idaho, which the Park Service had closed. After losing patience with Morrissey’s handling of the problem, Webster sends in Army Rangers, and in the ensuing battle many men die. The militia’s handsome leader, Thomas Porter, 34, escapes. He is a multi-billionaire with a past shrouded in mystery. The massacre on the mountain sets in motion a sequence of events that eventually leads to the secession of Idaho from the Union. As the country falls apart around her, Sarah McGill, 34, a rising television network star, finds herself falling in love with two men; a dashing Army officer, Jake Kincaid, 36, the son of the Speaker of the House, and the enigmatic Thomas Porter; and what makes this drama of the human heart all the more poignant is that Jake and Thomas are long-lost brothers.
And volume two:
Driven by emotion rather than logic, President Webster approves an ill-advised plan to kidnap Governor Morrissey using Army Special Forces. However, the attempt fails, which drives the governments of six other western states to secede and form the Continental States of America with Morrissey as its President. Eventually, President Webster is left with no choice but to declare war on the new confederacy. The brutal civil war that ensues lasts for seven days and involves the most ferocious and devastating tank battles in history. By the time it ends, the blood of over one hundred thousand soldiers has been spilled on the savaged soil of the sorrowed nation.
As I obscurely mentioned a few days ago I had freezing rain to drive through on the way to work last Monday. Here are a few pictures of the van after I arrive in the desert town of Richland Washington.
Then today I was doing some errands around town when my daughter Xenia and I saw smoke coming from across town. I dropped her off at home and went to get the oil changed in the van. The smoke was coming from only a few blocks away so I walked over and took a few pictures of the house fire. It was set deliberately by the fire department for training purposes and to get rid of an old house.
It is well known and widely accepted that homo sapiens are vulnerable to lasting denial-of-service attacks involving pyrotechnically accellerated projectiles.
Markus Kuhn, Computer Lab, Univ of Cambridge, GB
In a Usenet post:
Subject: Re: StegOS – taking steganography to the next level
Date: 2002-06-20 04:07:12 PST