- CM901 gains increased fire rate by attaching an underbarrel attachment (M320 or Shotgun), 667 to 750 RPM.
- Mk14 loses a minute amount of refire rate and drastically increases visual kick (not viewkick) by attaching an underbarrel attachment.
- The AS50 has a lower zoom level than the Barrett, even lower than the ACOG.
- The AK47 with the Hybrid Sight has a lot of move sway when ADS'd.
- The FAD loses ROF when an underbarrel attachment is added.
- The Riot Shield will stop showing cracks when Dynamic Environment is turned off (PC only). However, this will stop dynamic meshes from moving, so what someone could see could not be the same as what you could (example: Enemy shoots something off tabletop, it will disappear on his game but not yours).
- Extended Mags on shotguns will increase the bullet count by 1.5x AND the pellet count by 1.5x.
- The M4A1 has a very fast sway, compared to other guns.
- LMGs will now get 150 rounds per magazine plus 150 reserve ammo, effectively giving 300 rounds compared to 200 rounds in MW2.
- The Five Seven, when on Akimbo, has a very short reload time. Confirmed on PC.
- The Five Seven has a very short reload time when using Extended mags. Non-existent in PC, confirmed on PS3.
- The MP412 has a bigger hipfire box than the 44 Magnum and Desert Eagle, making it a poor choice when Akimbo.
- Secondaries only need 250 kills compared to the 300 on primaries.
- The Trophy System will stop up 2 to projectiles, and creates a much smaller explosion. This includes frags, semtex, flashes, EMPs, concussions, smokes, Predator missiles, Reaper missiles, AC-130 105mm shells, and AC-130 75mm shells. However, they must be rather close to the Trophy System.
- The Trophy System will trigger from throwing Ballistic Vests near it. Confirmed on X360.
- The EMP Grenade can destroy equipment on impact, though an explosion is enough as long as it is in the explosion radius. However, it will explode in mid-air after 1 second, and the radius is not very large.
- Knifing your own Trophy System awards credit for Sitrep Pro.
- Specialist will unlock all perks AND proficiencies. In turn, you will gain challenge credit from these, including those that are not unlocked yet. However, you do not get the Breath and Attachment proficiencies, or the Damage proficiency on non-Shotgun weapons.
- The Reaper has a limited amount of missiles.
- Juggernauts do regenerate health. Sticking them with Semtex is a one-shot kill.
- Osprey Airdrops will always drop one Airdrop Trap.
- The Recon Drone will trip Claymores and Bouncing Betties. Confirmed on X360.
- Recon will paint enemies with Lethal OR Tactical grenade explosions.
- Overkill will take into account your heaviest weapon, no matter which slot you put them on.
- Blast Shield will MINIMIZE the effects of Flash and Concussion, not completely negate them.
- Overkill Pro will disable the attachment proficiency on both weapons.
- Enemy killcams can reveal Airdrop Traps. If they have skulls on them, or it does not display an icon denoting what killstreak reward it is, then it is a trap crate.
- The Thermal Scope has a lower zoom level than the ACOG.
Too lazy to name, but most of this info comes from DenKirson's forums, as well as TmarTn's videos on YouTube.