The Engineer is a camping defender, and also a great defensive and sometimes supportive class to his team. His stock loadout, as always, Emphasize this as his Shotgun and pistol are good defensive weapons. First, The shotgun.
A Very well rounded weapon, the shotgun is what many veterans regard as the best stock weapon.
You probably know when to use it. When fending off attackers and supporting your teammates.
His secondary is the pistol. Another great stock weapon, don't write this weapon off because it's small you usually use this weapon when your shotgun runs dry or to finish off a wounded opponent.
Then, His melee.
An engi's wrench is a tool that besides being a stock melee weapons, can repair and level up his buildings.
The usual tactic with a stock engineer loadout is to fin a good spot and build a sentry nest. Then, upgrade the sentry and dispensers to max level. After that , camp in the area fighting off enemies with the shot gun, being ever careful to stay near the sentry nest.
