A fake Omega Seamaster 300M gives itself away at four points: dial printing, bezel action, caseback engraving, and the movement under the caseback. Check those four and you can separate a replica from a genuine watch in about ten minutes with a loupe and a kitchen scale. The "291" string you see in listings is a seller batch tag, not an Omega reference. Omega Seamaster 300M references run in the 210.30.xx.xx.xx.xx pattern, so any listing that calls 291 an official model number is mislabeling the product.

Tools and prep

  • A 10x loupe or a phone with macro mode
  • Digital calipers
  • A scale accurate to 0.1 g
  • Photos of a genuine Seamaster 300M from the same generation
  • A watchmaker who can open a caseback and run a pressure test

Step 1: Read the dial

  1. Hold the loupe over the Omega logo at 12 o'clock and compare the letter shapes to your reference photo.
  2. Read the "Seamaster" and "Professional" lines. Genuine dials carry raised, sharp type. Replica text shows soft edges and loose spacing.
  3. Check the date window at 6 o'clock. The genuine aperture has a polished bevel and the date sits centered in the frame.
  4. Tilt the dial toward a window and inspect the lume plots. Genuine Super-LumiNova sits flush inside the applied metal frames.

Step 2: Work the bezel

  1. Grip the bezel edge and rotate it one click at a time. Genuine 300M bezels index through 120 firm detents with no lateral play.
  2. Press down on the bezel at 6 o'clock and rock it side to side. Any vertical lift points to a replica insert and a weak spring.
  3. Compare the insert color to your reference. Genuine ceramic holds a deep blue or black with a matte finish. Replicas show a glossy or purple cast in daylight.
  4. Examine the lume pip at 12 o'clock. It should sit inside a raised metal surround that sits level with the insert.

Step 3: Measure the case

  1. Measure across the case at the 9 and 3 o'clock sides. The genuine 42 mm case reads between 41.9 mm and 42.1 mm.
  2. Measure lug to lug and case thickness. Genuine numbers land near 50 mm and 13.6 mm.
  3. Weigh the watch with the bracelet sized for your wrist. A genuine 300M on steel sits in the 195 g to 205 g range. Most replicas come in 10 g to 25 g lighter.
  4. Inspect the crown guards at 3 o'clock. Genuine guards curve into the case with a polished flank and no seam line.

Step 4: Study the caseback and helium valve

  1. Turn the watch over and read the engraving. Genuine text is stamped deep with crisp edges. Replicas use shallow laser etching.
  2. Look at the hippocampus relief. The genuine sea monster has defined fins, a textured tail, and a clear trident.
  3. Find the serial number on the lug at 7 o'clock and compare the last digits to the warranty card.
  4. Test the helium escape valve at 10 o'clock. The genuine crown has fine knurling and a two-position action.

Step 5: Inspect the movement

  1. Ask a watchmaker to open the caseback.
  2. Check the rotor engraving and the balance. Genuine Co-Axial calibers show Geneva stripes, blued screws, and a free-sprung balance.
  3. Place the watch on a timegrapher. Genuine Caliber 8800 beats at 25,200 vph, or 3.5 Hz.
  4. Confirm the power reserve. The genuine 8800 holds about 55 hours off the wrist.

Step 6: Check the bracelet and clasp

  1. Run a finger along the bracelet edges. Genuine links are polished on the outer faces with brushed flanks.
  2. Close the clasp and press the diver extension. Genuine clasps snap with a solid click. Replicas rattle and shift.
  3. Check end link fit at the lugs. Genuine end links sit flush with no gap or step.

Step 7: Pressure test the watch

  1. Take the watch to a watchmaker and request a water resistance test.
  2. Compare the result to the rated 300 m, or 30 bar, depth rating.
  3. Ask for the test result in writing before you buy or sell.

Where the 291 tag comes from

Sellers use short numeric tags to track batches without naming a factory. The 291 tag travels with a batch of replica Seamaster 300M watches, so it tells you nothing about the case, the dial, or the movement inside. Treat the tag as a listing label and judge the watch on the checks above. Note that selling a replica as a genuine Omega is fraud in the United States and most other markets, so keep the disclosure clear on any resale.