Remember the line from your last basic firearms safety course:
If the gun fails to fire, keep the action closed and pointed in a safe direction for a few seconds. It may be a hangfire.
So what does that mean when shooting a pump shotgun?
Well most pump shotguns have an Inertia Slide Lock just for that reason.
However:
The 1200,1300, Speed Pump and now SXP actions do not have an inertia slide lock:
The currently advertised Winchester SXP "inertia assist" is simply the lack of an inertia slide lock as present, for example, in the 870 and 500 series shotguns by Remington and Mossberg respectively. The original purpose of the inertia slide lock was to keep the action locked in the event of a quick hangfire (delayed ignition of the primer/powder). Hangfires were relatively rare even in late 19th and early 20th century ammunition. However, in shotshells constructed of wound paper, the possibility of a moisture induced quick hangfires apparently remained a concern. Accordingly, slide action shotguns continued to be designed with an inertia slide lock release. When the shotshell fired, recoil shoved the shotgun to the rear, the forearm assembly would by its own inertia move forward, this miniscule movement unlocked the slide allowing the action to open. The inertia lock function works so fast that most shotgunners are unaware of it. Should there be a quick hangfire the operator's hand pulling slightly rearward would keep the action locked. If so desired a slight hand induced forward movement of the forearm would also unlock the now hammer forward action ( both exposed or concealed hammer designs).
The forerunner of the SXP design, the Winchester 1200, was introduced in 1964. This was well into the transition to the, cheaper to mass produce, plastic shotshell bodies and fold crimp closures. In light of the, by then, virtually non-existant hangfire phenomenon, Winchester designers apparently omitted the inertial lock concept from the new rotating bolt design.
Does your slide action have an inertial slide lock?
Here is how to check:
Make sure your shotgun is unloaded, close the action and release the safety. Then in a regular firing position pull rearward on the forend and pull the trigger. If an inertia slide lock is present the action will remain locked until you allow the forend to move slightly forward and then pull rearward. If no inertia slide lock is present, the forend will move rearward as soon as the hammer drops.