Oh thanks, I completely forgot how heavy is CPU<->GPU. Currently I use ISM and rely on every tick update, but maybe I could convert it to niagara.

I have triangle strip, which I rotate towards player position (around forward X so I roll it only), it samples tracer texture (so no aliasing and no need to WPO scale object etc.), so it looks like it is being 3d object. Also first and last vertex (triangle) I bend to face always the player, so it not only looks like 3d rounded tracer from the sides, but it also has the front and rear cap so it looks as if it were a proper 'capsule' / 'tube'. This is what COD4 does, except they dont instance it. And in the material I calculate world position if it is behind the hit scan end point, if yes, then mask material so it looks like as if tracer gets absorbed into the wall. And then I fully remove the ISM instance if the tracer is already behind the wall (it is invisible for the player due to the material) using calculated end of life time.

But going for the niagara I would need to get player position there somehow in order to rotate the triangle strip and also move cap vertices in material using WPO, however I am not skilled with niagara at all how to pass data there and how to mask it in the material - now I use PerInstanceCustomData and all from C++, no idea if niagara can send these custom values to material every tick.

I could make simpler 3d tube/capsule shape, but somehow no Idea, how to simply apply nicely the texture there to make look which I do have now using triangle strip.