SUGGESTIONS:
Shock-And-Awe: Modified shotgun which shoots an electrically charged slug that causes the target to tumble, take damage over time, and potentially chain the effect to two other nearby enemy units.
Cold Killer: Modified sniper rifle that fires a liquid nitrogen capsule which freezes the effected unit in place for three seconds and causes them to take increased damage while frozen.
Caustic Personality: Modded grenade launcher that shoots acid grenades which create an area effect that slows and damages targets.
Small Package: A pistol that fires explosive darts which stick into an enemy or wall and detonate a few seconds later.
Bankswarm: assault rifle that fires ball bearings instead of bullets which ricochet a large number of times
Spitfire: SMG with incendiary bullets that have a chance of setting things on fire.
In terms of realism,
Shock-and-awe actually exists, without the chain effect.
Cold Killer would have to be an arrow gun
Small package would have to be a crossbow or a gas-oped pistol
Bankswarm's rounds would have to be made of tungsten for something like that to happen, and depending on what material it hits factors whether it bounces or not and how hard
Spitfire is just kinda out there, not possible, but I suggest explosive tipped rounds.
In terms of blocko
Chain effect would be hard to accomplish, sounds like the Wunderwaffe DG-2.
Freeze should slow them down, not completely kill them.
Caustic personality is pretty good idea.
small package sounds like black-ops bow on steroids.
Bankswarm-When do the bullets expire, and how many times will you shoot yourself?
Spitfire-Seems kinda Too OP should your player get hit by 5 bullets that set you on fire.