1st Instance[]
In the latest episode (at the time) and season finale, "Winner take all", Percy was able to dodge and block against multiple revolver bullets. Ones which Zora shot and then left in place before releasing her epithet to send them all flying. The dodging itself was considered Percy "dancing around the bullets" so it could be a very casual feats but this specific calculation will be on two instances of her blocking and dodging, lining up the two frames moved compared to the bullet in order to compare movements of the two.
https://youtu.be/CKKSkA2lKF0?t=859
This recalc will be using the speed of Zora's gun being 800 m/s. Because the Epithet Erased Wiki page for Zora showing her gun is being based on a Schofield revolver/Smith & Wesson Model 3.
In the first instance, Percy's sword moved 95 pixels and the bullet moved 255 px,
95 px / 255 px = 0.3725490196 times the muzzle velocity of the revolver
0.3725490196 * 800 = 298.03921568 m/s or Mach 0.868918996151604 (Subsonic+)
2nd Instance[]
Percy's sword movement: 175 px
Bullet moved before hitting her sword: 225 px
175 px / 225 px = 0.77777777777 times the muzzle velocity of the revolver
0.77777777777 * 800 = 622.222222216 m/s or Mach 1.814058956897959 (Supersonic)