The best ways to discover missing out on Weapons?: You can see the number of Hidden Weapons you have actually discovered by pausing the game throughout an objective, or by looking into your development in goal select.

It's suggested you play Battlefield 4 on easy difficulty mode, so that you can move the more congested levels easier. Otherwise you'll regularly get shot at when you're attempting to get an item you wish to accumulate.

Bear in mind that, Note: If you getting weapons from dead enemies it counts to your collectibles progress for the "Recon" achievement / trophy. It's not in fact required, however it does speed up the procedure to that trophy.