In the console first type "sv_cheats 1" to enable cheats and then input:

Sk_max_357 no.# .... The numerical value for no.# is new max ammo for .357 Magnum

Sk_max_ar2 no.# .... The numerical value for no.# is new max ammo for Pulse Rifle

Sk_max_ar2_altfire no.# .... The numerical value for no.# is new max ammo for Pulse Rifle energy orbs

Sk_max_buckshot no.# .... The numerical value for no.# is new max ammo for shotgun

Sk_max_crossbow no.# .... The numerical value for no.# is new max ammo for crossbow

Sk_max_grenade no.# .... The numerical value for no.# is new max ammo for hand grenades

Sk_max_pistol no.# .... The numerical value for no.# is new max ammo for pistol

Sk_max_rpg_round no.# .... The numerical value for no.# is new max ammo for RPG

Sk_max_smg1 no.# .... The numerical value for no.# is new max ammo for submachine gun

Sk_max_smg1_grenade no.# .... The numerical value for no.# is new max ammo for SMG grenades

Sk_plr_dmg_pistol no.# .... The numerical value for no.# is new damage value for pistol

Sk_plr_dmg_357 no.# .... The numerical value for no.# is new damage value for .357 Magnum

Sk_plr_dmg_ar2 no.# .... The numerical value for no.# is new damage value for Pulse Rifle

Sk_plr_dmg_buckshot no.# .... The numerical value for no.# is new damage value for shotgun

Sk_plr_dmg_crossbow no.# .... The numerical value for no.# is new damage value for crossbow

Sk_plr_dmg_crowbar no.# .... The numerical value for no.# is new damage value for crowbar

Sk_plr_dmg_grenade no.# .... The numerical value for no.# is new damage value for grenades

Sk_plr_dmg_rpg_round no.# .... The numerical value for no.# is new damage value for RPG rockets

Sk_plr_dmg_smg1 no.# .... The numerical value for no.# is new damage value for submachine gun

Sk_plr_dmg_smg1_grenade no.# .... The numerical value for no.# is new damage value for SMG grenades