I recently read about binding fov 90 and 110 to a key in order to "zoom" with pistol/lr/m4, what ever you want, would work with spas :D
anyways, 110 gives you the advantage to see more of your surroundings and 90 does support your aim since the targets are bigger. I wrote a few lines, dunno if one can do it better. Replace AUX1 (my side button on the mouse) with whatever key you want to use ;)
Code:
set fovzoom "vstr fovzoom1"
set fovzoom1 "cg_fov 90; set fovzoom vstr fovzoom2"
set fovzoom2 "cg_fov 110; set fovzoom vstr fovzoom1"
bind AUX1 "vstr fovzoom"
enjoy