Editor recommended because this is the officially named Prestige Attachment for ECHO 12. It is not labeled BEST. Tradeoffs are quoted from official launch copy.

ECHO 12
Barrel18” MFS Greyhound BarrelReach maximum Weapon Level and Prestige the weapon.
Specialized extended barrel to provide a massive improvement to bullet velocity with a slight improvement to ADS Spread and additional improvements to recoil control at the expense of damage range.
Attachments 1
- Barrel18” MFS Greyhound BarrelReach maximum Weapon Level and Prestige the weapon.
Specialized extended barrel to provide a massive improvement to bullet velocity with a slight improvement to ADS Spread and additional improvements to recoil control at the expense of damage range.
Alternatives
- Base weapon / no prestige attachmentKeep the base gunsmith path if you do not want the official prestige tradeoff quoted above.
Evidence basis: Source
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Recommended · bo7-echo-12-prestige-launch