How does the weapon unlock work in BF3?

[Jacco]

I've been playing for ~10 hours now and I JUST unlocked my first gun (to my knowledge). It was the PP90K or whatever- basically a useless weapon.
But I've been unlocking attachments for both the M16 and AK74. I don't get how it decides what you get and what you dont. I did a Google search but didnt come up with anything useful or that I understood.

Also, who's fucking bright idea was it to make it so you starting weapons level up separately?! I spawn on the Russian team like 80% of the time so when I get dropped into the American one, I'm screwed.

 

[mornal]

You unlock attachments for each weapon individually. If you unlock the ACOG for the M16, you still have to unlock the PSO (or whatever the 4x scope is for the AK74).

As for what attachments you unlock, the weapon's page on battlelog has all of it's attachments in the order you unlock them.