Using a FET would be pretty cool!
I set up my cutdown for the current measurement. I used my DMM on the 20 A scale. When I made the connection, the DMM spiked around 5 A. After a several seconds, it settled in around 4.25 A.
The cutdown power supply for the nichrome is three Energizer Ultimate Lithium AA batteries. The energized length of nichrome is about 3/4 inch. I used 26 AWG nichrome 80.