Flamethrower that relies on the fire grenades from H3 for ammo, it's a basically a super soaker that shoots greek fire but if you charge it fires a shotgun blast of the stuff with a strong burst of air. it sould require reloads and not be like the UNSC flamethrower; I would say this would make sense as a brute weapon.
The recycled plasma core shotgun; it's basically a shit load of plasma pistol cores strapped to a longer platform and all hooked to one trigger. Pros: long range, high rate of fire, high shield damage Cons: overheats quickly, slow projectiles, low health damage
I think a good starting place for balancing this thing would be 4-5 rapid shots before having to manually cool it, 2 shots would be a kill assuming all projectiles hit; you'd want to dump 3 quickly to compensate for the spread leaving you with one or 2 shots if there is another person coming for you. I wouldn't recommend a charge option here.
RUKT: Tartarus' hammer from H2 as a legendary weapon; it would be a gravity hammer with a short range projectile attack that consumes a large portion of the battery.
A a barrel over barrel brute long riffle with a two shot burst meant to replicate the AN-94 in real life but using a simpler principle and consequences of that principle. Because it's barrel over barrel it would have an irregular spread model as the two rounds will cross over each other in the air; these round of course being the caseless spike rounds like those seen in the spiker itself. It would be deadly accurate with 0 horizontal spread and it's projectiles would follow the same predictable vertical spread route and the cross hair should be designed to show this, something like a series of "8"s getting smaller and then bigger and this can be shown with probably 4 "8"s each thinner or more transparent.
Needle rifle and carbine arguable fill the same role, I would differentiate them by giving the Carbine it's halo 2 fire speed and comparable damage and give the needle riffle The H4 carbine rate of fire but the needle riffle would have 2 twists, It's full auto but the fire rate would be a hair slower than the carbine when held down second the round lose their high velocity after about 35 meters and gain tracking.
The bolt shot is no longer a spawn weapon and needs a reason to exist now. My suggestion is to change it's charge function, up it's semi auto damage a wee bit, and when charging instead of it being charged and firing half of it's bullets make it commit bullets to the charged shot the longer you hold it, eventually when you get to the second to last bullet it's reached a no return and is going to charge the final bullet no matter what; when the charge ends it will automatically discharge a single shot that behaves like the binary rifle's and destroys that particular bolt shot upon firing.
I think the damage increase on ADS for the Light riffle is crappy, instead keep the mechanics of the weapon and make it the only weapon that doesn't knock the player out of ADS on being shot, it's scope does break apart and cover your face when you aim down.