After completing a few missions you will return to your shed where you can see all the weapons that you have collected. For this trophy you will need to have all Firearms collected and on display. A Firearm is any weapon that fires bullets, Melee weapons such as Knives and Golf Clubs do not count towards this trophy. Some weapons are concealable and some are not; some weapons are unique to certain missions, whereas others can be found in pretty much in all missions and some you can get by getting the Silent Assassin Rating.
Not Glitched: There is a common misconception that this trophy is glitched because people have collected all Firearms but the trophy has not popped. This is because since you have collected the last Firearm, you have yet to return to your shed. You will need to actually go there and see everything on display for it to be recognised, then the trophy will pop. For example: If you collected the Custom Rifle and it was the final weapon you needed, then the trophy will not pop at the end of the mission because you have yet to return to your shed. You will have to replay the first level and wait until the shed opens and when it does then the trophy will pop.
When you choose your difficulty which you want to play the game on, there is no way you can change your difficulty without having to start from scratch with a new save. See 'Saves and Difficulty' in the Roadmap for further information.
Warning: If you lose a weapon which you have got through getting the Silent Assassin Rating, then it may not be recoverable and you may have to restart your game.
There are 3 vital points which you will need to take into account when trying to get this trophy.
For a weapon to be 'collected' you must carry it all the way to the end of the mission. It is not the simple case of just picking it up and bang, it is in your collection. For the small weapons that are concealable you won't have a problem, it is the much larger weapons such as the Assault Rifles, Shotguns and so on (which are clearly visible) that may cause a few problems when completing a mission. For example: If you are dressed as a Russian Soldier they tend to carry an AK 47 so if you are trying to carry a different weapon such as a Shotgun to extraction, then clearly this kind of weapon is not part of the soldier's uniform. Problems can arise if you are trying to maintain cover because getting too close to a soldier will result in your disguise being blown. Be prepared, as sometimes it may be necessary to use trial and error and the odd restart to work out the perfect route to ensure that the weapon is brought home safely. Lastly if you are killing a guard in order to get his weapon/disguise then make sure his body is well hidden otherwise, if found, the guards will be looking for a 'Suspicious' person wearing that particular disguise. Furthermore it is strongly recommended that you kill the guard you are acquiring the weapon from as opposed to sedating him. This is because if you do not extract quickly, the unconscious guard will awaken and run around naked telling everyone, then they will be on high alert!
You usually return to your shed after completing all the missions in that particular country, which usually stretches from 3 to 5 missions depending on what country you are in. This does not mean if you pick up a two handed weapon (which is not concealable) that you have to carry that weapon all the way through that country's remaining levels until you return to your shed. The weapon is automatically stored in your shed as soon as you complete the level you acquired it in, despite you not returning to your shed. For example: If you pick up the Crossbow in the Hidden Valley and complete the mission, because you do not return to your shed when you start the next level (At the Gates) you will still have the Crossbow in your possession. You are, however, at liberty to drop the weapon and you will not lose it out of your collection. Please also note that dropping weapons which are concealable such as handguns, will cause you to lose them unlike the weapons that are not concealable. Lastly in the final mission you have the option to return to your shed during the level and stock up on weapons to help you complete the level. Note: If you drop these weapons, you will not lose them from your collection.
If you are using Level Select to clean up the remainder of the weapons, before you start any missions you will be on a briefing screen where Diana will give you info about the contract. You will also get the option to take weapons into the level. As good as this sounds it's really a double-edged sword because if you were to drop one of the weapons here, you will lose it and as a result you will have to acquire it again. Furthermore if you re-pick up a weapon which you already have in your collection then drop it, you will not lose it. If you have already acquired the Deagle (Desert Eagle) and you re-pick it up in another mission, then you are at liberty to drop it without fear of losing it from your collection.
Although you can shoot your way to extraction, it is very risky especially if you are playing under Professional Difficulty. It is highly recommended that you take the stealthy path to ensure that you carry the weapon home safely. Getting the right disguise and making your way to extraction is equally important as finding the gun itself. See the gun trophies below for a written and video guide for all the Firearms. Also see the Roadmap for a checklist you can use to keep track of weapons and what level they can be obtained in.