Long distance target shooting

I’m looking for recommendations for a two way radio system that will transmit the sound of a lead bullet hitting a steel target from distances of up to 1200 yards. The idea is to put a vox acuated radio behind the target (for protection) and another non-vox acuated radio at the shooters location to be able to monitor hits on the target. Misses can generally be seen thru a spotting scope due to the dust cloud created by the bullet impact but a hit is not visible at that distance. Bullet flight duration is approx 4 seconds so a hit on the steel target would be easy to hear if I can figure out a sound activated system that would transmit a “hit” vs a miss. With the exception of the radio being behind the target, transmission would be line-of-sight. The radio at the target could be placed on some sort of mount not attached to the target but within 12 inches. Will something like a Motorola MR355 work??
Also, a shooting session usaually lasts up to four hours so I would need that much operating time on the battery pack if possible.
Thanx in advance for any suggestions!

Can’t think of any VOX that would have the kind of response time you seem to be looking for.

Most VOX HTs I’ve used have to be exposed to a trigger level sound for at least .5 second, which in terms of shooting, is an eternity in which the event has long since occurred.

The targets are made of 1/2" thick plate steel and are circular 34" diameter suspended from two chains. Though I have no way of knowing what the duration of the sound (ring) is, I suspect it is more than .5 seconds.