Heres a quick way to test the burn rate (BR) of time fuse and how to properly set and time a timed delay in mutable shots. What is burn rate? BR is an average burn time in a given length of fuse. In this Instructable I will sub jest you use factory made fuse ( with a BR of 35 to 45 seconds per FT.) Seeing how home made fuse will have imperfections and working with explosives that is not something you want to get wrong. Why would I want a delay? When we were setting breaching charges, we needed to get in the house quickly and off the streets. with a delay we were able to have some stand off distance from the door. Here is what was taught to me when I was working with demo in the marines, this is straight from my books, I hope after this you can safely do what I love and blow stuff up.
the stuff you'll need
role of fuse ( in my case its string)
sharp cutting device
pen and paper
Step 1: TESTING BURN RATE
To test the burn rate of time fuse, you must first cut off six inches from the roll and discard it. this ensures that any moisture the time fuse may have been exposed to will not effect the test of the burn rate. Next you will cut off three feet. it is very important that your measurements are precise so that you can get an accurate burn rate. You will now need to ignite one end of the fuse to determine the amount of time it takes to burn three feet using your stop watch. Once the time fuse burn is complete, you need to take the total time and convert it into seconds and then divide that number by three. This is getting an average burn rate per foot, which will be your final burn rate. IF THE NUMBER HAS A DECIMAL, then you will round to the nearest 100th. Remember, your BR should be 40 seconds per foot with a tolerance of plus or minus 5 seconds per foot. (working with m700 time fuse)
Step 2: CUTTING TIME FUSE
After you have tested the burn rate of the time fuse, measure and cut it at a length that will burn in the desired amount of time. To do this you have to take the desired time delay and convert it into seconds.
Step 3: DO THE MATH
Next you need to take that number and divide it by the BR for that roll of time fuse.
Step 4: CONTINUE THE MATH
The number to the left of the decimal is your desired feet of time fuse. Now you will find the amount of inches you will need, so you will take the number to the right of the decimal and multiply it by .12, this will give you the remainder in inches.
Step 5: FINAL ANSWER
The number to the left of the decimal is inches. Since, in the example, there is no number to the left of the decimal, then the correct would be 0 inches. No we have 7 feet and 0 inches. We want to get the number down to the lowest possible form, So now we need to find 1/16 of an inch. We will now take the number to the right of the decimal and multiply that by .16
The number to the left of the decimal represents your 1/16 of an inch, and the number to the right of the decimal will not be used. This gives us a final answer of 7 feet and 5/16 of an inch. When cutting the time fuse, ensure you pull the fuse tight along the tape measure, if its loose, this can effect your total time.