Is gunSlinger the meaning of a gunman?
If we do some quick math here to compare the two you will see that gun cancels each other out in both of the words and you are therefore left comparing slinger and man. To my knowledge I have never seen either of these words use to represent each other and therefore it is my educated guess that the final answer is no.
I’m not sure how this is a support topic.
That aside, no, these words are not strictly speaking synonymous; gunslinger implies great skill with guns, while gunman implies criminal/killer with a gun.
One throws guns
the other is made of guns