You can also just delete the WAE1XXX1.ACM from the "data\sound\sfx", and the gunshot was decreased in volume because it was the equivalent of ear rape.
Would that just replace it with the original? Now I feel dumb. Oh well, whatever.
Like I said, though, I get why it was replaced, most people thought it was too loud (although I didn't, guess I never had Fallout on very high volume). Most people are not everyone however and people like different things. I liked the super loud boom, it gave the impression of a bigass bullet through a pistol. Made perfect sense to me all along. So I'd say it'd be a good idea to make it one of the options in the installer instead of just including it automatically, just like everything else is an option in the installer (including other sound effects). Obviously not a top priority but it would be nice for the fraction of the Fallout people who like loud pistol noises for their giant pistol shots.