Yah I found this last night looking too
Years Ago™, I asked Marty about this.
He said "If I sang about Herwin & Hulbert nobody'd know what I was talking about and it doesn't exactly roll off the tongue anyway. Besides I don't want to appear to be advertising any one particular brand over another.
And anyway, you don't think for one minute Columbia's gonna let me get away with singing about a 'Bad A$$ .44' do you?
I never knew if he was pulling my leg with that answer or not. With him it was hard to tell.
But it made perfect sense to me.
It seems that Marty had always liked the long sleek look of the long barreled Merwin & Hulbert revolvers. And since most of them were nickled plated they looked even sleeker.