Revolver, Pistol, Handgun
noun
A fist gun is a small fistish sized gun that has some punch (because, you know, fist!). The gun I'm describing is a revolver, or a handgun.
けんじゅう
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
私は拳銃を派手なスパンコールで飾り付けしてみました。
I decorated my revolver with flashy sequins.