Battlefield Hardline is a game of many strategical players, with that said; you always want to be on your A-Game when using your favorite weapon, you've probably already spent numerous hours trying to get in sync with multiple weapons to find your fit with your play style, it's all a mystery.
The bad thing is that the weapon attachment descriptions on Battlefield Hardline aren't very informative. So when you put a grip and sight onto your weapon and it feels pretty good to you, but are you really getting the most out of your weapon? Maybe another attachment combo could further your range/accuracy/damage etc further beyond that of other players? There's no real way to determine your attachment before spending your money; with can result in a well-selected item or an utterly useless purchase.
Well now, at least there are some bits of information released, to settle your troubles. Thanks for the Battleifled YouTuber, TheRussianBadger, you can find all of such information into a single video, which is posted at the top of this thread.
If you want to dig deep into the details of the video, and what exactly the YouTuber is explaining, the statistic page is here.