Hi all.
Thought I'd share the Ballistic Curve that I'm using to snipe with, in Black Ops 4:

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I'm an old school sniper and find it quite difficult to quickscope, so I needed help from my Apex in order to stay on target in middle-distance gunfights.
This curve works really well.
My micromovements are unaffected so that I don't over compensate when I'm shooting at long distance and my fast swipes, to snap onto target, are unchanged. The strength of the curve is that it reduces my mouse's sensitivity a little at normal ADS movement speed to give me a bit more control. I increased my ADS sensitivity by 25% to compensate so that I'm moving my reticle around more quickly other than when I'm focused on tracking a slow moving target.
With it, I'm getting headshots with relative ease and am much more confident about getting Diamond camo quickly for the snipers.
Oh, and it works fine if you're using any other weapon, just might need to tweak the Activation Delay as the animation is different for the different weapon categories. I don't. Can't be arsed.

I know someone will ask

so here are my settings. They won't necessarily be the best ones for you ('cos you're not me!) so play around with them to find your sweet spot:
Mouse :1000 Hz, 3200 DPI
Apex: 250 Hz
Manager settings for ADS config:
- Black Ops 4 ST
- Activation delay: 224
- Smooth Aim Transition: Off
- Aim sensitivity: 10
- Sync: Common
- Smoothing: 0
- Y/X Ratio: 1.25