Omega · Omega 3861

Omega Speedmaster Moonwatch Professional power reserve: inside the calibre 3861

Every current Omega Speedmaster Moonwatch Professional, including the Hesalite and sapphire models, the white dial, the Silver Snoopy and the First Omega in Space, runs on the hand-wound calibre 3861. A full wind lasts about 50 hours, just over two days.

Updated September 2026 · Based on manufacturer specs, published reviews and watchmaker/owner reports

Watches that use the Omega 3861

If your Speedmaster Moonwatch says "Co-Axial Master Chronometer" on the dial, or it was bought new after January 2021, it has a 3861. Omega debuted the movement in the 2019 Apollo 11 50th Anniversary editions and put it into the regular Moonwatch in 2021, replacing the 1861. Unlike before, the Hesalite and sapphire models now share the same movement and finishing.

The skeletonised Dark Side of the Moon "Apollo 8" and Grey Side models use the 3869, a derivative. The Speedmaster Racing, Dark Side of the Moon (automatic) and Speedmaster Pilot use the automatic 9900 instead.

Specs at a glance

History and where it came from

The Moonwatch was the last big gap in Omega's modernisation. From 2015 Omega moved its range to co-axial, METAS-certified "Master Chronometer" movements, starting with the 8900, but the Speedmaster Professional kept its hand-wound 1861 with a Swiss lever escapement. The 1861 itself was the 1968 calibre 861 renamed in the 1990s.

Omega's answer was to modernise without changing the watch's character. The 3861 keeps the cam-operated chronograph, the horizontal clutch, the manual winding and the 3 Hz beat, and it looks close to the old movement through a display back. Inside, the Swiss lever escapement is replaced by Omega's co-axial escapement, the hairspring is silicon, and the balance is free-sprung. Jewel count went from 18 to 26, the reserve from 48 to 50 hours, and for the first time in the Moonwatch's history the seconds hack.

It appeared first in the gold and steel Apollo 11 50th Anniversary editions in 2019, then in the 2020 Silver Snoopy, and became the standard Moonwatch movement in January 2021. That launch also brought a thinner case, a dot-over-90 bezel, a step dial and a new tapered bracelet. Monochrome measured the Hesalite model at 13.6 mm against 14.3 mm for its predecessor.

Accuracy in the real world

This is the biggest practical difference from the 1861. Every 3861 Moonwatch is tested as a cased watch by METAS to Omega's Master Chronometer standard: 0 to +5 seconds a day, plus function in a 15,000-gauss magnetic field. The old movement had no chronometer certificate at all.

Owner reports on watch forums are generally positive about new 3861 watches. Like any Master Chronometer figure, it's measured under test conditions, so position and how you wear it will move the number a little. The silicon hairspring means everyday magnetism from phone cases, laptop speakers and bag clasps shouldn't knock it off, which was a common cause of sudden gains in older Speedmasters.

A 3 Hz balance is slower than most modern chronographs. On paper that gives up a little stability, but the free-sprung balance and certification make up for it, and the slower beat is part of why the reserve stays at 50 hours in a compact hand-wound movement.

Reliability and servicing

The mechanical layout is more than fifty years old, so the chronograph side is thoroughly proven. The co-axial escapement and silicon parts are newer, but the same technology has run in Omega's automatics since the 2000s.

• Warranty. Omega's current product pages list a five-year warranty against material and manufacturing defects.
• Brand service. Omega's own service network handles it and can restore Master Chronometer performance. Omega describes the co-axial design as needing less frequent service than a conventional chronograph, but it still needs servicing eventually.
• Independents. Co-axial and silicon parts are supplied only within the Swatch Group network and to approved watchmakers. An independent who happily services 1861s may not be able to get 3861 parts.

Quirks worth knowing

• It hacks now. Pull the crown and the small seconds stop, so you can set it to the second. Owners coming from the 1861 often don't expect it.
• No date, no danger zone. Without a date there's nothing to damage by setting it late at night.
• Still manual wind. There is no rotor. A day on the wrist doesn't wind it, so it stops about two days after its last wind.
• Wind to resistance, not beyond. You'll feel the crown firm up when it's full. Stop there.
• Chronograph use. Leaving the chronograph running takes extra energy, so it will run a little short of 50 hours if you do.

How it compares

• Omega 1861: the previous Moonwatch movement. Same look and layout, 48 hours, no hacking, no chronometer rating and a conventional steel hairspring, but simpler for independents to service.
• Omega 9900: Omega's automatic chronograph, with a column wheel, vertical clutch, date and 60 hours. It's in the larger Speedmaster Racing and Seamaster chronographs.
• Rolex 4130: the Daytona's automatic chronograph, with 72 hours and a -2/+2 s/day Superlative Chronometer rating. A very different, self-winding watch.
• Zenith El Primero 400: the high-beat 5 Hz automatic chronograph, with about 50 hours of reserve.

Living with the 50-hour reserve

With a hand-wound Moonwatch you manage the reserve yourself. Wind it every morning until you feel the resistance and it will never stop, because you are topping it up long before the 50 hours are used.

The question is what happens when it isn't your only watch. Wind your Speedmaster at 8am on Friday and take it off that evening for a weekend in your Seamaster, and it will stop around 10am on Sunday. Put it away for a week and you'll be winding and setting it again. Unlike an automatic, wearing it doesn't help, so a watch box of automatics and one Moonwatch always ends with the Moonwatch stopped first. Watch Winder counts down the reserve for each watch you own, from your last wind, and reminds you before it stops. To check a trip or a long weekend, try the "Will my watch stop?" calculator.

Verdict

The 3861 is what the Moonwatch needed: the same hand-wound, cam-operated chronograph that owners love, with a certified 0/+5 s/day rate, strong magnetic resistance, hacking seconds and two more hours of reserve. It hasn't changed how you live with the watch: you still wind it and it still runs about two days. The trade-off is servicing, which in practice means Omega or an approved watchmaker rather than any chronograph specialist. For most buyers that's an easy trade.

FAQ

How long does the Omega Speedmaster Moonwatch run after winding?

A current Speedmaster Moonwatch Professional with the calibre 3861 runs for about 50 hours from a full wind. Winding it once a day keeps it running indefinitely.

Does the Speedmaster Moonwatch 3861 hack?

Yes. The 3861 stops the small seconds when you pull the crown to set the time. It's the first regular Moonwatch movement that does.

How accurate is the Omega Speedmaster Moonwatch Professional?

The 3861 is a METAS Master Chronometer, tested to run between 0 and +5 seconds a day. That is a test of the whole cased watch, not just the bare movement.

Is the Speedmaster Moonwatch automatic?

No. The Moonwatch Professional is hand-wound, so it needs winding every day or two. Omega's automatic Speedmasters, such as the Racing and the Speedmaster Pilot, use the 9900.

How do I tell if my Speedmaster has the 1861 or the 3861?

3861 watches say "Co-Axial Master Chronometer" on the dial and have references starting 310. Pre-2021 Moonwatches with the 1861 have references such as 3570.50 or 311.30.42.30.01.005.

Does the Silver Snoopy Speedmaster use the 3861?

The 2020 Silver Snoopy Award 50th Anniversary does. The earlier 2003 and 2015 Snoopy editions use the 1861.

Is the 3861 Speedmaster antimagnetic?

Yes. It is certified to keep working in magnetic fields of 15,000 gauss, thanks to its silicon hairspring and non-magnetic components.

Sources

• Omega: Speedmaster Moonwatch Professional 310.30.42.50.01.002
• Monochrome: All the details about the new Speedmaster Moonwatch Professional Master Chronometer
• Monochrome: Speedmaster Moonwatch Professional white dial
• Monochrome: 2024 Speedmaster First Omega in Space
• WatchBase: Omega caliber 3861

Keeping it running

• Wind it fully once a day, at the same time, until you feel the crown stop. Never force it past that point. Can you overwind it?
• A full wind lasts about 50 hours, so winding every morning keeps it running with time to spare.
• A watch winder can't wind a hand-wound movement, so it needs you instead.
• If it does stop, don't set the date between 9pm and 3am. Check if it's safe.

All Omega movements

Never let it stop

Watch Winder counts down the reserve of every watch you own and reminds you before one stops. It already knows the Omega 3861: type your watch's name and the reserve fills itself in.

Manufacturer's published figure. Real reserve varies with the watch's age and service; check your manual.