edit 5/11/15: extreme edit found most of the best attachments for legendary weapons
[b]full list open to interpretation [/b]
[u]Auto Rifles[/u]
[b]RED DOT - ORES = 0.3x optics, +6 Range, +9 Stability, +4 Reloading, +4 Handling [/b]
[u]Pulse Rifles[/u]
[b]RED DOT - ORES = 0.3x optics, +6 Range, +9 Stability, +4 Reloading, +4 Handling [/b]
[u]Scout Rifles[/u]
[b]RED DOT - ORES = 0.3x optics, +6 Range, +9 Stability, +4 Reloading, +4 Handling [/b]
[b]RED DOT - OAS = 0.2x optics, +14 Stability[/b]
[u]Hand Cannons[/u]
[b]TRUESIGHT - IS = +5 Stability, +8 Reloading, +8 Handling [/b]
[u]Fusion Rifles[/u]
[b]RED DOT - OAS = 0.2x optics, +14 Stability[/b]
[b]RED DOT - ORES = 0.3x optics, +6 Range, +9 Stability, +4 Reloading, +4 Handling [/b]
[u]Shotguns[/u]
[b]AGGRESSIVE BALLISTICS = +5 Damage, +6 Range, +9 Stability [/b]
[b]FIELD CHOKE = +5 Damage, +12 Range, -15 Stability [/b]
[u]Sniper Rifles[/u]
[b]Ambush SLH25 = 0.5x optics, -15 Range, +20 Stability, +10 Reloading, +12 Handling [/b]
[b]EagleEye SLR20 = 5x optics, +20 Range, +5 Stability, -8 Reloading, -8 Handling [/b]
[u]Rocket[/u]
???
[u]Machine Gun[/u]
[b]AGGRESSIVE BALLISTICS = +5 Damage, +6 Range, +9 Stability [/b]
if you have anything to add let me know