Simple enough, here is what is unlocked at what level on xbox live multiplayer.
Default: MP5K
Default: M16
Default: Olympia
Default: HK21
Default: Dragunov
Default: ASP
Default: M72 LAW
Level 2: M1911
Level 4: Makarov
Level 4: Create A Class
Level 5: Contracts
Level 5: Enfield
Level 6: Clan Tag
Level 6: RPK
Level 7: Skorpion
Level 8: Stakeout
Level 8: Game Mode Challenges
Level 9: M14
Level 10: Killstreaks, Killstreak Challenges, Playercard Emblems
Level 10: WA2000
Level 11: Mac 11
Level 12: RPG
Level 13: Combat Record
Level 14: Famas
Level 15: Ballistic Knife
Level 15: Medal Challenges
Level 16: Gun Emblems
Level 17: AK-74u
Level 18: Python
Level 18: C275 (When Declassified)
Level 19: Gun Tag
Level 20: Elite Challenges
Level 20: Galil
Level 21: M60
Level 21: Stoner63 (When Declassified)
Level 22: Camo
Level 23: Uzi
Level 24: Spas-12
Level 24: HS-10 (When Declassified)
Level 25: Custom Reticules
Level 26: AUG
Level 27: L96A1
Level 27: PSG1 (When Declassified)
Level 28: Custom Lenses
Level 29: PM63
Level 30: Final Challenges
Level 30: Strela-3
Level 31: Face Paint
Level 32: FN FAL
Level 33: Crossbow
Level 35: MPL
Level 38: AK-47
Level 41: Spectre
Level 41: Kiparis (When Declassified)
Level 44: Commando
Level 44: G11 (When Declassified)
Level 48: China Lake
Level 50: Prestige Mode
Prestige 1: Prestige Leaderboard
Prestige 1: Custom Class 6
Prestige 3: Custom Class 7
Prestige 5: Custom Class 8
Prestige 7: Custom Class 9
Prestige 9: Custom Class 10
Prestige 11: Face Tattoos
Prestige 13: Clan Tag Colors
Prestige 14: Golden Camo
Prestige 15: Prestige Playlist
