Question about a curious observation. My 640-3 has seemed to run very well, although I only fire it intermittently. I noticed that when I dry-fire it (with snap caps) I can sometimes see a small spark behind the upper cylinder in the area of the firing pin. This can occur with snap caps or an empty cylinder. I assume the spark is from the fp striking metal in the frame. Is this within normal limits, or is it a sign of some significant problem?

Smith & Wesson revolvers have a titanium bushing pressed into the frame that the firing pin passes through

The spark is from the two metals striking each other

All of the modern revolvers do this to some extent

A set of quality snap caps will reduce the sparking if you are troubled about metal being removed

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"Acta non verba"

I believe you are correct. I just researched the issue and it appears this is not rare, and has been observed in several models of J frames with frame mounted firing pins. Someone posted a video of this on You Tube in 2009. Theories include spark due to air compression within fp channel providing enough heat to ignite lubricants - kind of dieseling effect? Anyway, several commenters many yrs ago said that S&W was aware & stated it was normal & did not result in abnormal wear or damage to components. In any case, an interesting phenomenon.
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