My weak side ear is worse.
My understanding is that the ear that is most nearly directly behind the gun (typically the strong side ear) benefits from some cancellation effects.
In addition, if you shoot rifle or shotgun, your strong side ear is not only directly behind the bore, it's also turned away slightly and "shadowed" from the muzzle blast by your head. The same effect can be seen, though to a lesser extent when shooting a handgun two-handed. One handed pistol shooting is probably the exception in that the strong-side ear is turned slightly toward the pistol.