Although he looks slow and stupid, the Heavy Weapons Guy is an expert in the use of... heavy weapons. He carries a huge gun known as the assault cannon. It has a 200 round clip and slices through enemies like butter. While the recoil of firing such a weapon would probably kill lesser classes, the HWGuy is able to withstand it easily. However, the recoil is still rather powerful and firing the assault cannon does cause the HWGuy to slow down considerably. The gun is most effective at close to medium range, and quickly loses accuracy at long range. Due to the combined weight of his weaponry, armor, and self, the HWGuy moves very slowly.
Since he likely carries well over 200 pounds of gear (and is slightly overweight himself), the HWGuy is hard to push around with explosions. This makes the HWGuy effective at defending choke points. Since he can't easily be knocked out of them, the enemy has usually no choice but to either die to assault cannon fire or retreat. If you want to be an impenetrable (and deadly) wall, the HW Guy is the class for you.
The standard-issue crowbar for every class. It does some damage, but not enough to make a difference in a battle against a full-health opponent. It's a good humiliation tool for someone who is about to die, however.
Pathetic damage, but it has a tight spread, so it's better than the Super Shotgun at long range.
Use this if you don't have enough time to wind up the assault cannon, or need maneuverability: for example, if a Spy is trying to backstab you.
Takes a couple of seconds to rev up, but does good, continuous damage up to medium range. The HWGuy is slowed considerably when firing it.
A standard fragmentation grenade.
A tactical grenade that releases a large, spherical high-gravity field. The slowfield will slows down any enemies that walk through it. It is very effective against enemies moving at high speeds, as it brings them to a crawl.
Additional Strategy and Tips
Playing Against an HWGuy