Somebody dug deep into Planetside 2 and finally figured out exactly what the attachments do. It's in a
spreadsheet here. A few things are missing, like min/max damage drop off values and pistol attachment stats. But here's what everybody has always wanted.
Some interesting things:
-Aside from hiding your flash, flash suppressors don't actually do anything positive. They don't reduce the distance you get spotted on the minimap by anything. At all.
-Suppressors drop velocity by 20% for SMGs, 35% for carbines, and 40% for all other guns, except the Railjack which drops the velocity by 50.05%. It also changes the damage curve, but by what and how much isn't known.
-HVA increases velocity by 5% for most guns and increases vertical recoil by 10%. There are exceptions where HVA changes the velocity by a value different than 5%. E.G., the TRAC-5B's velocity gets boosted from 490 to 600 and the Gauss Rifle Burst's velocity gets boosted from 650 to 650. It also changes the damage curve etc. etc.
-SPA decreases velocity by 5% in all cases, and changes the damage curve by some unknown values etc. etc.
-Compensators decrease vertical recoil by 15% in most cases, increase hip cone of fire by 20%, and increases the spot distance on the minimap by 35m in all cases. Most guns are normally spotted at 40m and LMGs are spotted at 50m.
-Foregrips reduce recoil by 25% in general cases, 33% for advanced foregrips, but there are a lot of specific exceptions. It also increases the equip time (the time between changing from a different slot to that weapon).
-Laser sight improves hipfire by 33%, 40% for advanced laser sights. Pistols are exceptions.