In This Little Guide I Will Be Posting All The Required Levels For All The Weapons And Perks And What It Takes To Get Attachments.
And My Current Level. Which Changes By The Day.

My Current Level: 55

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Primary Weapons
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Assault Rifles
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1. M16A4 - You Get It From The Start
2. AK-47 - You Get It From The Start
3. M4 Carbine - Level 10
4. G3 - Level 25
5. G36C - Level 37
6. M14 - Level 46
7. MP44 - Level 52

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Sub Machine Guns
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1. MP5 - You Get It From The Start
2. Skorpion - You Get It From The Start
3. Mini Uzi - Level 13
4. AK-47u - Level 28
5. P90 - Level 40

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Light Machine Guns
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1. M249 SAW - You Get It From The Start
2. RPD - You Get It From The Start
3. M60E4 - level 19

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Shotguns
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1. W1200 - You Get It From The Start
2. M1014 - Level 31

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Sniper Rifles
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1. M40A3 - You Get It From The Start
2. M21 - Level 7
3. Dragunov - Level 22
4. R700 - Level 34
5. Barret .50 Cal - Level 49

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Side Arms
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1. M9 - You Get It From The Start
2. USP .45 - You Get It From The Start
3. M1911.45 - Level 16
4. Desert Eagle - Level 43

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Attachments
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1. Red Dot Sight - Get 25 Kills In Totall
2. Silencer - Get 75 Kills In Totall
3. ACOG Scope - Get 150 Kills In Totall

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Special Grenades
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1. Flash Grenade - You Get It From The Start
2. Stun Grenade - You Get It From The Start
3. Smoke Grenade - You Get It From The Start

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Perks
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Perks 1
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1. C4 x2 - You Get It From The Start
2. Special Grenades x3 (No Smoke) - You Get It From The Start
3. RPG-7 x2 - You Get It From The Start
4. Claymore x2 - Level 23
5. Frag x3 - Level 41
6. Bandolier - Lever 32
7. Bomb Squad - Level 14

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Perks 2
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1. Stopping Power - You Get It From The Start
2. Juggernaut - You Get It From The Start
3. Sleigth of Hand - Level 20
4. Double Tap - Level 29
5. Overkill - Level 38
6. UAV Jammer - Level 11
7. Sonic Boom - You Get It From The Start

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Perks 3
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1. Extreme Conditioning - You Get It From The Start
2. Steady Aim - You Get It From The Start
3. Last Stand - Level 8
4. Martyrdom - Level 17
5. Deep Impact - You Get It From The Start
6. Iron Lungs - Level 26
7. Dead Silence - Level 44
8. Eavesdrop - Level 35