I wouldnt do that unless you want to risk scaring your dog from eating...the loud noise may be associated with eating and the dog might get scared...
Try taking the dog out and having someone else shoot with a small caliber gun about 100yds away and moving in making shots at small increments say every 15 yds or so..
you basically will have to comfort the dog and do just like a brand new pup, and break him into the gunshot again..