Thanks for the responses.
I am not trained in DSP, but I have already been experimenting with hardware to process the impact, and am quite confident that I am most of the way there on that. Moving forward, assume there is a clean pulse coming from each microphone. If I can accomplish this in the RPi without it slowing things down too much, then I would incorporate that, but that would be later.
I am new to Python, but my son is a whiz, and he will be helping with that. The target is actually for him, as he is a competitive shooter. I have also done some work in C, but limited. If there is a language that would be ideal for this, I am open to learning a new one.
The pellets range from 4.48 - 4.51mm in diameter. The target is 17cm square. I don't know if I can post links here so google "issf pistol target".
Yes I am primarily needing to measure time difference, but in the nanosecond range. 1us gives a resolution of 0.343mm so 100 ns would be 0.034mm which is enough. I was also thinking of using interrupts for each microphone, so on port change, a timestamp would be saved for each one in its own variable. The first impact would be saved as "time 0" and used as a reference, and each successive one would be a greater value. After that, it's just math to calculate the impact position.
I know how to do this in PIC microcontrollers, but the ones I am familiar with aren't fast enough to get the resolution that is needed.
Thanks in advance.