MudD is correct that you can just turn them off. If the molds are a good fit … they do cushion the sound some. Most likely … your Phonak will require you to open the battery case to shut it off.
If you're almost as deaf as a doornail (like me) … you could just yank 'em out and probably still not hear anything.
I found all the "auto" type features (like the cut off) extremely annoying and had them all disabled. Even so …. I'd probably remove the aid closest to the gun for the air compression/concussive blast (hopefully no muzzle blasting). Why rattle 'em if you don't have to ?