Trying to apply physics to One Piece in the first place is your mistake
The M3 have been "calced" as Bullet Timers since fucking East Blue. Yet despite being 1000 chapters into the story and Characters being dozens of times stronger than East Blue Luffy Guns are still treated like a threat that most people would barely avoid.
The In Story answer is that the stronger the sniper is the faster his bullet
How? I don't fucking know, ask Oda