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