Search:

Clearly range isn't the weak link. 2km is ample.

Yes, good point. I was assuming zero other noise, which in hindsight isn't practical.

There's also the thought that a sound detector/mike installed nearby to catch the ring of a struck plate might work.

It wouldn't have to be on the plate, just close enough to work well enough.

If it was 22 only, no problems I should think.

Potentially a good idea.

The only problems I can forsee are vibrations through the plate shaking the sensor too much leading to failure, and a projectile pass through causing the sensor to go ...