yah, there's a smidge of plausibility burried beneath head-scratchingly awful justification. Literally just take a power drill that's controlled by an AI chip that won't activate unless put against a rock formation
I should def have written "resonance gun" since sonic gun is what the mechanism boils down to, but the Uhm Ashkulaly excuse for why it can totally obliterate solid rock but not blast apart a clearwater slug is the specific frequency of the soundwave