Welcome! The photo has the appearance of lead residue from firing, but if that is actual erosion into the cylinder face I would contact factory customer service for advice. The Ti alloy cylinders have a protective coating on them to prevent/retard this from happening, but if a previous owner removed it with abrasive cleaning that would explain the damage. It has also been noted to occur with unscrubbed cylinders, however, and fortunately replacement cylinders are still available.

If you shot 400 full power .44 Magnum loads through in 3 sessions, you are quite the determined shooter! Hope this is helpful.

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Alan
SWCA LM 2023, SWHF 220