Easiest COMBAT
Shotgun build would be to buy a pump shotgun from a store IN THE BOX (this is required for the "build")... open box, remove stock/receiver/mag tube assembly and the loose barrel... Partially open action, insert barrel into orifice above mag tube.... insert fully using moderate human pressure... now this is very important... twist in a clockwise rotation, the barrel retaining screw or mag tube cap (this varies with make and model) using the dynamics on the pre machined helical incline plane (this will be known as threads) to reduce the gap from bottom of screw head or mag tube cap until sufficient torque/force is attained. Do not use wrench or pliers as it may mar the finish and/or exert excessive force on barrel, receiver, mag tube, barrel retainer screw or cap and could even cause damage to the helical incline plane on mag tube and/or retaining fastener device...
Upon completion of the above steps... A kinetic test, void of multi component pre assembled projectile equipped destructive assemblies (known by lesser sophisticated individuals as "ammunition"), should be performed by applying locomotive physical activity to the moving parts that cause the functions of the various components of the combat device to complete their designed functions including pressure to the release lever retaining the thin hardened section of ferrous metal in it's compressed position to determine that all of the individual components of the combat capable projectile emitting assembled device function according to design parameters and in required harmony.
Following this extensively sophisticated functionality research and testing, The installation of the aforementioned pre-assembled projectile emitting assemblies should be performed with caution so as not to install an excessive quantity of these devices so as not to exceed the predetermined compressed length of the helical wound compression resisting cylindrical shaped pre stressed section of ferrous metal linear strip.
Now by applying locomotive physical activity to the moving parts that cause the functions of the various components of the combat device to complete their designed functions including pressure to the release lever retaining the thin hardened section of ferrous metal so it makes expedient and forceful contact with the detonation component of the projectile emitting destructive assembly, with the device directed towards an approved receiving component also known as a target, launch the projectiles in a linear fashion with high velocity motion.
While doing this repeatedly, also take this time to replace chemically formulated protective coatings from the requisite components and replace them with metallic colored exposed surfaces void of any amber or brown colored oxidized coatings on said metallic surfaces...
It will take many repetitions of the aforementioned locomotive repetitious cycles...
OKAY.... consider your self lucky... I have never used such sophistication or thorough detail to assist anyone with their combat shotgun needs!
Brent