He won't be a problem to your shrimp or crabs. I've even had crabs slide down into the pistol's hole and seen him push them right back out - now of course unless he's in his building mode and wants to wedge the crab somewhere in there for a wall. I could happen I think, but you should be alright.
One thing you wanna be sure of is that your LR
is touching the bottom of the tank glass. If not, as he tunnels he will cause rocks to drop of course, either hurting himself or starting an avalance of stacked rocks.
What is "shooting" by the way?