So, I found out that there are codes which work for any account.
M60 machine gun
Enter try4ndrunf0rcov3r as a code.
QBU88 sniper rifle
Enter your3mynextt4rget as a code.
USAS12 shotgun in multi-player mode
Enter aw3somef1rep0wer as a code.
Uzi
Enter cov3r1ngthecorn3r as a code.
And they actually worked.Just tested out the sniper code and I didn't even preorder the game.These codes work for ANY account.
I already had all 4 of them except the sniper.