Bon, pour ceux que ça intéresse, j´ai trouvé ça sur GAMEFAQS.com, donc tout est en anglais mais au moins c´est expliqué de manière précise.
Melee Mayhem Award
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Find every melee weapon in the Game, and despite the name, apparently also all
firearms. You only have to pick them up, but I suggest swinging them once
to make sure the game does count it. If you still have problems unlocking the
Award try killing at least once with every weapon.
I covered all of the weapons for you with specific locations for not so common
weapons. I´ll walk them through in order of the chapters they can be found in,
this does not mean they can only be found in that specific chapter though.
Check Firearm Freedom Award for the guns:
Chapter01 - Rebar Conrete,Conduit,2*4Nails,2*4Bolts,Fire Axe,Large Pipe,
- ****** Small Pipe,Rebar Bent
-Conduit: In the room after you lost your gun
-Rebar Bent: In a locker opposite of the fireaxe-door with the TV in it.
-Large Pipe: On a rack in the same room with the Rebar Bent.
-Rebar Concrete: In the last room of the chapter, sticking out of a pillar.
Chapter02 - Shovel,Rebar(straight),Crowbar,Mannequin arm
-Rebar: Check the bin near the flasks you need to investigate.
-Mannequin Arm: In a bin after you opened the 210 door with a sledgehammer. If
you missed it, Barts Department Store has em all over the place
.
Chapter03 - Sign
-Signs: Check walls for Signs
Chapter04 - Steam Pipe
-Steam Pipe: Your 1st or 2nd Encounter(crawlers) carries one. Or grab it from a
wall near the manhole with 2 crawlers coming out of.
Chapter05 - Clothes Rack
-Clothes Rack: An inch away from that mannequin head down in the basement.
Chapter06 - Locker Door
-Locker Door: At the start of this chapter, check for the yellow lockers that
can be found throughout chapter08, the school.
Chapter07 - Paper Cutter, Gaspipe, Desk Drawer, 2*4 burnt
-Desk Drawer: After Rosa found the Masterkey and you enter the office room, its
right in front you when entering the room.
-Paper Cutter: Same room as the desk Drawer, on the far end.
-Gaspipe: Sure can be found in earlier chapters, thing is I can´t remember
where. Probably Chapter04. Anyways: After you got the Intel about
the School(end of chapter), one of the guys attacking you holds one.
-2*4 Burnt: After falling down to the basement, check the walls for a burnt
piece of wood.
Chapter08 - Desktop, Handrail
-Desktop: Right at the start, check the childrens desks in the corridor.
-Handrail: On the wall next to the Bird you found in the boys´ toilets.
Chapter 09 - Stick, Large Plank, Fireplace Poker
-Stick: Ninjas hold these. Finish the one in the attic off to get one.
-Large Plank: When you head down the stairs into the basement, at the end of
the stairs look on the workbench in front of you.
-Fireplace Poker: Around the fireplace in the living room.
Chapter 10 - 2*4 Fire
There are other weapons, which you will pick up automatically in the course of
the game, being: Fireplace Poker, cleaver and a rod with bolts from a subway
train(Handrail). Additionally you´ll need the Fireaxe, Shovel, Crowbar and the
Shovel for advancing the story. Don´t forget to pick up the upgraded Taser Rosa
brought you along in Chapter07. Please note that the Fireextinguisher cannot be
picked up, thus is not classified a Melee Weapon. The longer Stick "The Hate"
is wielding cannot be picked up either.
NOTE: This is not verified but you might wanna use every gun as a Melee Weapon
once, to make sure you get the Award. Press RB to switch from ranged to melee
with a gun.