I have an unfired 638-1 that I can barely press the thumbpiece forward to release the cylinder. The thumbpiece itself moves freely after the cylinder is swung out so I'm sure the problem ? involves the center pin or spring. Has anyone encountered this? If so, can I do something to it without having to return it to S&W?
Thank you in advance for any input you can give me.

Could be degraded lubricant, etc, inside the cylinder assembly, extractor rod, and/or the front locking bolt, preventing the center pin from moving freely inside the cavity. I've noticed some very long (heavy) center pin springs inside J-frames recently also, which would only make the problem worse.
You could try removing the cylinder assembly from the yoke and either soaking or disassembling the internals to free up the center pin.
If it's the front locking bolt that is sticking, a bit of solvent on the bolt and lug should solve the problem.

Yoke mis-alignment could also be an issue, but is less likely. This misalignment can put stress on the center pin inside it's cavity in the breechface.

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Ret. LE, FA Instr, S&W Armorer

I've spent most of this AM looking for actual specs on the center pin spring. Every site visited claims to have run into long. or heavy springs but, how do I know if that is my problem? Is there a certain length listed somewhere for that spring?

You should be able to tell by the pressure on the center pin in this particular assembly, compared to your other revolvers. (if you happen to have other to compare it with)

Open the cylinder and try to press the center pin forward with your finger. If there is an unusual amount of resistance on the pin itself....or more that the "normal" spring pressure, it's either from something inside the cavity in the assembly, (extending through the inside of the extractor and the extractor rod) like dirt, debris or old degraded lubricants, a damaged or bent center pin....or from an excessively strong center pin spring.

I have seen many J-frame assemblies fit with very long center pins, which could be the issue, if you have ruled out everything else. If you are unable to check the status of the components by disassembly, you could always contact S&W Customer Service and send the gun in for a check up. I've included a photo below of the difference in the available center pins.

I believe the longer springs for the larger "magnum" calibers/frames sometimes make their way into the J-frame assemblies.

Attached Images

IMG_1697b.jpg (220.0 KB, 17 views)

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Ret. LE, FA Instr, S&W Armorer

Have you checked to see the ejector rod is screwed all the way In?

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H Richard
SWCA1967 SWHF244

Yes, thank you H Richard. It's tight.

Thank you armorer951. Looks like i"m sending it in. I guess everything doesn't have an easy fix.