Shooting works in a couple ways. There's ray-traced shooting, and projectile-launching shooting, that's just what I call them, probably not proper terminology.
With ray-traced shooting, you track a line from the end of the gun barrel straight out until it hits something. Then you place textured plains around the gun barrel to make it look like fire, and you animate stuff along the invisible line from the barrel to the object it's pointed at, then you make an effect on the object the line collided with like a decal or explosion. You can then deal damage to the target if it applies.
With projectile-launching you have a bullet object, position it at the gun barrel, and just move it forward and forward and forward until it hits something.
That's kind of a rough ouline, see what you can get with it and keep posting.
Crazy Donut Productions, Current Project: KillZone
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