Does anyone else feel uncomfortable putting the deadly force of a firearm trigger behind a low pressure switch and a solenoid?
Be aware that a solenoid plunger is heavy (you've shown a large solenoid- nearly 1/2 lb overall!) and free-floating. If it is bumped or shaken hard enough, the inertia of the plunger's mass can be enough to push the trigger and fire the weapon. Disconnecting the battery will not help this.
A pressure switch can also be fooled by a number of things, most common is kinking the tube. Impact/vibration on the sensor has some potential to affect the output as well.