Marksman/spotter help?
My first advise is; Don't try to be the high score hero (Mr. K/D, A nerd with 50cal rifle, etc). This is not what I want from recce (marksman spotter team)
1st. priority when you are playing recce is not to be seen or heard, adding suppressor doesn't take away the sonic boom from the bullet.
2nd. priority is to provide intel for the front line. This means you have good overview of the AO.
There is still more but the shooting part is the last.
If you adapt this, you're free to move to next part. You have to learn to enjoy to be useful for the big picture, not for you score. <-This is how I play as recce.
Well, Shooting is fun when you can take down targets up to 1500m with 100% accuracy. This requires actual skill and knowledge.
Lets talk about Weapon platforms. I always take the lowest caliber that does the job. 7.62 nato for non body armour targets inside 900m (vanilla m14). .338 LM (L115a3 or Noreen URL) for 500m to 1500m or targets with body armour. .50 cal is only for nerds, too loud, too heavy and usually it's better idea to use the HMG

. 1 rule: learn the platform and make sure it works with ace3 ballistics. (vanilla and 3CB rifles works)
Other gear that you need for accurate fire is
Vector 21 rangefinder, Kestrel 4500 weather unit. ATragMX ballistic calculator, A range card just in case. I'm not goin to the details because i want to keep this post short and there is a lot of stuff in youtube covering this.
Keep your kit light! My sniper kit is >25kg
Sometimes I use the public server to practise my skills but I make sure there's no major action going on.
This may sound bit rude but it's my way to separate nerds with high caliber rifles from actually useful players who understands intel is the first element of warfare, movement is the second. and combat is third. And recce is <80% intel 15% moving to position and >5% shooting things.