Ok, I’m just starting to attempt to use the Plasma Caster. Trying to figure out the best situations to use it.
Similar to grenade usage? Thanks
aim it in the direction of people then FIRE EVERYTHING, this should kill at least one person 
Only try to stick a spartan if they are unaware/about to kill you/are using a ghost in one place. It’s more of an ambush weapon than anything else, with explosions easier to dodge than ever.
If a person is close shoot at you’re feet. normally a charge would be the best if you know there are enemies coming but the semi thing is good for unpredictable situations.
Guide to using Plasma Caster:
Step 1: Switch to a different weapon.
Step 2: Profit.
In all seriousness, I would only use it in a base defense kinda situation in Warzone, kind of like a shotgun pretty much. Hide around a corner and when someone comes, charge it up, pop out and try to hit them with it. 
Thanks, I’ll use the advice, I got taken down quickly in open field with it. I’ll stick to Base defense only with this weapon.
I just stick it on top of a ceiling on the door way, cause when they walk through boom, bunch of grenades explode on them. That’s if you are camping. LOL
A few tricks:
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A fully-charged shot that sticks to an enemy Spartan will kill them from full shields. If you plan to do this, have the weapon pre-charged before sticking your neck out so that you don’t get rekt by headshots.
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When scoped, charged nades will have a tracking effect against vehicles. It does decent damage, which lets the weapon be sort of a sort-counter to light vehicles. This is a great way to troll vehicles with exposed drivers such as Warthogs and Ghosts. You can often kill the driver this way, especially if using that Scourge of Fire variant…
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Ever have one of those times when you see a lot of angry red blips flapping around on your motion tracker around a corner? That’s the best time to use a Plasma Caster. If you can get some spam around the corner at the angry mob, you can/will kill several of them without them even seeing you. Armories and other locations that are being actively contested by both teams simultaneously are especially ripe for Plasma Caster spammage…
It’s all about knowing where your enemies are, and then using angles to get the plasma to where they’re at. The shots bounce really well, and have a decent blast radius. Spam some shots against a wall to get them around a corner, or off of the ceiling to counter a high ground advantage an enemy might have.
Think of the plasma caster as a frag granade launcher (only that is plasma) the ammo fired has a very similar physics effect.When I use it against an enemy that is directly in front of me I shot to the floor as the ammo has an ricochet effect and it usually lands is enemy’s face. And the charged mode works as a big plasma granade.