I agree that a squib is due to a low or non-existent charge of powder. On the subject of "light primer strikes" consider the following. It is not likely that pistol primers vary widely in the amount of striking force necessary to ignite them. On the other hand, rifle cartridge primers can intentionally be made heavy because most rifles do not have a firing pin spring. The firing pin flies forward and doinks the primer during chambering.
Getting to the point on pistols, if you have light primer strikes on any round of good ammunition then you are getting light strikes on all rounds. Some of the rounds go off, but all your strikes are light. The most common cause is too much headspace. In other words, the primer is too far away from the firing pin. Once in a while the symptom is due to insufficient primer seating. Firing pin energy is expended in moving the primer further into its seat in the primer pocket. Inadequate primer seating is typical of almost all consumer presses that do priming.
Assuming your primers are seated in the pocket (.002" - .006" below flush is typical), then you must look at the headspace in your gun. Revolver or pistol, there may be too much unsupported brass. The light primer strikes are an early warning sign which leads to blown cases later on. Unfortunately the fix for too much headspace in a pistol is a new barrel, and might even require a new cylinder in a revolver.
Armchair gunsmiths often purchase light mainsprings in order to achieve a lighter trigger pull. However, a light mainspring also reduces the energy transferred to the firing pin and to the primer. All these things should be checked. Bad ammo is the least likely reason for no ignition.
WM