How do you unlock the HOLO scope for your weapons on battlefield 3?

I know you have to complete an achievement or get a certain amount of kills, but does anyone know the exact number of kills or what achievement?How do you unlock the HOLO scope for your weapons on battlefield 3?
I only renember to get HOLO for M4A1 and AK74U : 50 kills

I almost forget how to get HOLO ( us and russia ) for almost every weapon.

But I can give u this :

1. Every weapon in BF3 has HOLO sights. Exept pistols

2. U need to kill people for engineers : 50 kills to get one

3. To unlock 1 attachment at a time, u can see under the current ammo that there is a progress bar. Every time u kill someone, the progress bar increases from left to right. If the progress barr is full, u get 1 attachment. To make the progress bar full from left to right, u need to kill only 10 people. So in ur M4A1 after u unlock the HOLO, u already have 4 more attachments. Which is :

1. Reflex RDS : 10 kill

2. Laser sight : 20 kill

3. Foregrip : 30 kill

4. Flashlight : 40 kill

So, do u understand this? Every time u kill 10 people, u get 1 attachments no mater how many attachments u have like is MW2 and MW3.

3.