that's not the way to go at all you really think forcing the dog to hear multiple shots that its already scared of is good advice..
To my mind that's like putting a child in front of a horror film on repeat and having the mentality of ohh they'll get used to it...
Makes no sense to me
Like i said stand off from the noise this will determine what your up against, the same as you said,thenwork from there
Did you beleave the person who you got the dog off,it sounds like hes had the same problem,its going to take along long time,try taking it to a gun club and stand off and let the dog listern to the noise,and lots of prase,good luck