Short answer

A replica Blancpain Fifty Fathoms with the 5050 case shape sells for $280 to $900. A genuine Fifty Fathoms Automatique in steel lists near $16,000 to $18,000. The fastest test is the power reserve. The genuine calibre 1315 runs about 120 hours on three barrels. Most replicas carry an ETA 2824 clone or a Seiko NH35 and stop after 38 to 42 hours. Wind the watch, set it down, and check it two days later. A dead watch is not a 1315.

What 5050 refers to

Listings use 5050 for the 45 mm Fifty Fathoms Automatique case, the family that includes reference 5015. Sellers mix numbers. Some print 5050 on a 42 mm case. Measure the case first. A 45 mm Automatique measures 45 mm across, about 15.4 mm thick, with 23 mm lugs. A 42 mm case with 22 mm lugs does not match that family. Photos hide scale. Ask for a caliper shot next to a ruler.

Movement checks

  • Power reserve. Genuine calibre 1315: about 120 hours. Replica 2824 clone: 38 to 42 hours.
  • Beat rate. Both run at 28,800 vph, so the rate does not separate them.
  • Finishing. Genuine bridges show hand anglage and circular graining. Replica bridges show straight machine lines.
  • Rotor lettering. Genuine engraving sits deep and sharp. Replica text reads shallow and flat.
  • Component count. The 1315 is reported at 227 parts and 35 jewels. A 2824 has far fewer.

Case, dial, and date

  • Date placement. The 45 mm Automatique puts the date near 4:30. Replicas on a 42 mm case shift it or drop it.
  • Date font. Compare the disc against catalog photos. Replica discs use wider, thicker numerals.
  • Dial text. Fifty Fathoms and Automatique should sit level with the markers. Replica printing sits low or uneven.
  • Caseback. Genuine sapphire casebacks show the movement. Engraved reference and serial sit crisp.

Bezel, crystal, and lume

The genuine bezel holds a sapphire insert with lume under the surface. Replicas use printed sapphire or ceramic with lume applied on top. Lume on the genuine dial glows for hours. Replica lume fades in 20 to 30 minutes. Check the bezel action. A solid, even click points to a better build. A loose, gritty turn points to a cheap one.

Papers, serial, and price floor

Genuine watches ship with a signed warranty card and a numbered certificate. The serial on the card matches the caseback. Replicas reuse one serial across a production run. Ask for a photo of the caseback and the card together. Import rules matter too. Counterfeit watches are subject to seizure at the U.S. border, and trafficking in counterfeit goods carries criminal penalties under 18 U.S.C. 2320.

What replicas get right

Good replicas copy case dimensions, dial layout, and crown guards at a glance. The gap shows in three places: movement, lume, and finishing. Those three items need a tool, a dark room, and a 48-hour wait. Anything else is photography.