for all "normals" i'll be using the five seven as standard...

P99 = melee animation is faster than normal

USP.45 = melee speed is just slighlty faster than normal, using tactical knife on it may mess up the iron sight alignment, I also realized this is not exclusive to the usp and all pistols seem to lose correct alignment when the tactical knife has been used at least once, apparently this is only visual and should not affect actual accuracy

.44 MAGNUM = melee speed is faster than normal

SKORPION = x2 head multiplier instead of 1.4
PM9 = same as skorpion

FMG = melee speed is slightly faster than normal

G18 = melee speed is faster than normal

RSASS = melee is slightly faster tan normal

STRIKER = both the melee animation and the recovery from it are the fastest in the game

RPG7 = the melee is apparently as fast as the striker, it also deals more damage than a regular melee

C4 TRIGGER = the melee deals more damage (apparently twice the normal damage, you can notice this in survival where a guy with ACR would normally take 2 meles to kill, but with the trigger it only takes 1, pending test with rpg7)

MP7 = Insanely accurate when aiming down the sights, i haven't tried this yet but i read once that thermal sight make it even more accurate.

CM901 = it has higher fire rate with a shotgun attachment (not sure about G launcher)

FAD = 95% run speed, x1.7 head multiplier

MK14 = Visual recoil increases when you add the shotgun attachment, however, it decreases when you add the Grenade Launcher attachment, this does not affect actual accuracy since it's just visual. 1.5 head multiplier instead of 1.4

MG36 = Slower firerate if grip attached

RIOT SHIELD (SURVIVAL) = It does not block bullets from behind like in multiplayer

BLAST SHIELD + RIOT SHIELD (MULTIPLAYER) + PRONE WITH THE SHIELD ON YOUR BACK = it will potentially deny a predator kill if you're hit directly on the shield, but it will leave you critical, not very practical but this combination protects quite good against the predator blast damage.

UMBRELLAS (MAP ASSET) = they block predators if hit on top of it

MODEL1887 = without upgrades it could deal between 150 and 240 points of damage, plus it has the second best range of all shotguns (usas12 has the best range)

USAS12 = increases sprint duration

DETONATING C4 WITHOUT USING THE TRIGGER = press f twice xdxd

scar-L: according to user 'clocas' the scarl has the fastest reload