It returns the scope to battery after each shot. Scopes like that slide back and forth in those mounts due to recoil, without the spring they have to be manually returned into battery after each shot. A lot of scopes (Unertl, Fecker, Lyman, etc.) used on centerfires purposely don't have the spring because the slam-bang action can wreck the really really fine crosshairs- not a big deal on light recoiling rifles. For example, the 8x Unertl's used on the WWII USMC M1903 Springfield sniper rifles had the springs left off on purpose for that reason. Some say it's a benefit, some say it's hogwash. Boils down to personal opinion, as always. I keep the springs on for some of the .22's, none on any of my centerfire target guns.
"You can lead a man to logic, but you cannot make him think." Joe Harz "Always certain, often right." Keith McCafferty
