Sellita RDM+ Optimization Barrel

On December 17, 2020, Sellita published R&D technical commutations / specific information sheets (No. 25 and 26) with regards to optimization barrel SW3XX-1 and SW5XX aka the RDM+ barrel.

In Sellita’s own words:

“In order to increase the power reserve of the SW3XX-1 movement family, we have developed a barrel with better performance. This new barrel, called “RDM+”, is recognizable by its exterior closure.”

And…

“In order to increase the power reserve of the SW5XX movement family, we have developed a barrel with better performance. This new barrel, called “RDM+”, is recognizable by its diameter of the axis.”

When did the SW300-1 and SW500 start using the RDM+ barrel?

The optimized barrels became standard in newly produced SW300-1 movements around January/February 2021.

What it means for SW300-1 movements:

Before this upgrade existed, the SW300-1 was quoted as having a power reserve of up to 42 hours on a full wind. This is consistent with the runtime of the ETA caliber 2892-A2 which the SW300-1 is based on.

With the new RDM+ barrel, the minimum runtime on a fully wound SW300-1 has been improved to 50 hours, with a typical power reserve of 56 hours. You may see some watch brands give quotes within this range, depending on how they want to market their watches.

SW300-1 Barrel Interchangeability:

The old 42 and new 56 hour barrels are interchangeable within the SW300-1 framework. In fact, after the new barrel was announced, some microbrand watch companies began offering service upgrades to the new barrel.

If you want to change your 42 hour barrel to the newer 56 hours version, use the part number below:

• New/56: 020.010.00065
• Old/42: 020.010.00018

Note that only the complete barrel with the mainspring is interchangeable in it entirety, not individual barrel components.

Is the new SW300 barrel interchangeable with ETA 2892-A2?

This is still unconfirmed See comments below! If you have experience fitting the new barrel in an ETA 2892 without issues, please comment.

In the meantime, let’s consider the fact that the old barrel was interchangeable and many parts sellers list replacement barrels as being compatible between the SW300-1 and ETA 2892A2. Of course, the barrel bridge is not interchangeable, as the Sellita bridge has a jewels for the barrel arbor, but this doesn’t seem to impact the barrel design itself.

What this means for SW500 movements:

Before this upgrade existed, the SW500 was quoted as having a power reserve of up to 48 hours on a full wind. This is consistent with the runtime of the ETA/Valjoux caliber 7750 which the SW500 is based on.

With the new RDM+ barrel, the minimum runtime on a fully wound SW500 has a typical power reserve of 62 hours.

SW500 Barrel Interchangeability:

The old 42 and new 56 hour barrels are interchangeable within the SW300-1 framework. In fact, after the new barrel was announced, some microbrand watch companies began offering service upgrades to the new barrel.

If you want to change your 48 hour barrel to the newer 62 hours version, use the part number below:

• New/62: 020.010.00110
• Old/48: 020.010.00025

Note that only the complete barrel is interchangeable in it entirety, not individual barrel components.

Additional Resources:

• Official Sellita SW300-1 RDM+ information (pdf)
• Sellita SW500 RDM+ information (pdf)

If there are other Sellita calibers with optimization barrels available, please add them in the comments section.