Sorry But NO
Battlefield 3 does have Co-op mode, you can also unlock weapons for use in Multiplayer from playing Co-op.
Unfortunately, no. The games are not ranked, therefore you can have access to unlocks on single player games.
-aw3somef1rep0wer will unlock the USAS12 Shotgun in multiplayer. That's the only cheat to unlock weapons (that I know of).
You must play Multiplayer and get experience to "Level Up" and after a certain amount of level ups you can unlock new weapons for kits.
In Battlefield 3 online multiplayer, the player can unlock weapons and other gadets by gaining points. The "C-4 Explosives" unlock for the Support class is unlocked by gaining 4000 score as the Support class.
The last unlock for every class is the other teams weapon for that class.
You must play Multiplayer and get experience to "Level Up" and after a certain amount of level ups you can unlock new weapons for kits.
Use every weopon once in single player mode
In Battlefield 3 online multiplayer, the player can unlock gadget by gaining points. The "SOFLAM" gadget exclusive to the recon class is unlocked at 26 000 recon score. The SOFLAM is an immobile laser designator that can 'paint' enemy vehicles for guided weapons.
In Battlefield 3, the player unlocks the UMP -45 Personal Defense Weapon at level 16. In real life, this weapon is classified as a submachine gun, in the game it falls under the Personal Defense Weapons category which include submachine guns and is available to all classes.
In Battlefield 3 online multiplayer, the player can unlock weapons by gaining points. The SPAS-12 is a pump action shotgun that is featured in the "Close Quaters" expansion. It is unlocked by completing the "These Hurt Too" assignment. This assignment requires the player to get:20 kills with Pistols20 kills with Shotguns
In Battlefield 3 online multiplayer, the player can unlock weapons, attachments, vehicles specializations, squad specializations and other unlocks by gaining points and completing assignments.Points can be gained by killing enemy players, capturing flags, arming M-COM stations, healing, repairing and rearming teammates, etc.Assignments are objective-based tasks that the player can complete to unlock a specific weapon, weapon camouflage scheme, vehicle specializations or dog tags. Assignments are only available in the expansions - Back to Karkand, Close Quarters, Armored Kill, Aftermath and End Game - and to those who have Battlefield Premium.