Short answer

Omega has no Seamaster 300M reference number that ends in 291. Reference numbers for the line start with 210 on models from 2018 to now, and with 2531, 2220, 2254 or 2532 on models from 1993 to the 2010s. The 291 tag appears in resale listings and forum threads. No Omega catalog and no factory sheet names it. Treat 291 as a seller or batch label, not a model code.

What the genuine Seamaster 300M is

Current model, 2018 and later

  • 42mm steel case. Water resistance 300m.
  • Calibre 8800. Co-axial escapement, silicon balance spring, 25,200 vph (3.5 Hz), 55-hour power reserve.
  • Master Chronometer grade. METAS runs 8 tests over 8 days and checks magnetic resistance to 15,000 gauss.
  • Ceramic dial with laser-cut waves. Date at 6 o'clock. Sapphire caseback.

Earlier models

  • 2531.80, sold from 1993 to 2006: 41mm case, calibre 1120, 28,800 vph, 44-hour reserve, date at 3 o'clock, aluminum bezel insert.
  • 2220.80, 2254.50 and 2532.80 share the same case family with different dials and bracelets.
  • All 300M models carry a helium escape valve at 10 o'clock.

Checks on a watch sold as a 300M

  1. Beat rate. Calibre 8800 runs at 25,200 vph. Most replica movements, including ETA 2824 clones and the Miyota 9015, run at 28,800 vph. A timegrapher gives the number in seconds.
  2. Movement view. The 8800 has a silicon balance spring and a rotor stamped with the Omega symbol and 8800. Copies show printed text and a bridge shape that does not match.
  3. Identification code. Modern Omega watches carry a 14-digit PIC on the caseback. Sellers reuse one code across a batch, so two new watches can show the same digits.
  4. Lume. Genuine dials use Super-LumiNova that glows for hours. Copies fade in minutes.
  5. Helium valve. On a real 300M the valve screws down and works. On copies it is a fixed cap or a dummy screw.
  6. Case metal. Steel cases weigh more than plated brass. A 42mm steel 300M on a full bracelet sits near 190g.
  7. Bezel and crystal. Genuine ceramic inserts hold markings that sit flush. Copies show raised paint and a hazy sapphire.
  8. Price. A new 300M lists above $5,000. Replicas sell for $200 to $600. No seller holds genuine stock at a tenth of retail.

Legal note for US buyers

Counterfeit watches are illegal to import into the United States under 18 U.S.C. Section 2320. CBP seizes shipments and can assess a civil penalty. The personal-use exemption does not cover goods that carry a copied trademark.

If a listing uses 291

Ask for a photo of the reference between the lugs and the PIC on the caseback. A 2018 model reads 210.30.42.20.xx.xxx. A 291 tag returns no data from Omega. The term stays unverified.