I have a newer SW 638 and today I had a FTF because the firing pin was failing to protrude beyond the frame.  

I assumed it was lint but then noticed it would still occasionally fail to travel far enough.  

I’m pretty familiar with SW internals so I took it apart.  Here’s my question:

The hammer block is present but is basically free to travel. There is no pin on the rebound slide to sit within the oblong hole at the bottom of the hammer block.  It almost appears the rebound slide is for a 442/642, which I don’t believe has a hammer block.

Is the 638 supposed to have this combination of parts?

642 would have the same hammer block. I can’t think of an S&W revolver since about 1943 that came without the hammer block safety.

You should have a pin in the rebound slide that controls the hammer block.

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You can probably google up some parts numbers to see if they are the same - I would almost say certainly that they are.  Perhaps the rebound slide pin was not installed (stuff like that happens).

If you can’t figure it out, I do have a 642 in the garage I can open up and photograph for you tomorrow.

Thanks.  

Midwest gun works has two different rebound slides listed. One specifies for an exposed hammer.  One has a pin and one does not.  Link

It would seem like a hammer block installed without the pin on the rebound would could lead to a circumstance where the hammer block could move up when it’s not supposed to.

Hmm…well I just opened up my 442 (early 2000’s vintage) and it definitely does not have a hammer block.  

Also, looking at rebound slides on Midways site it specifies the part with the pin for the 38 and 638.  It specifies the one without the pin for the centennial models (442,642, etc).

Is that your 638 in the photo?  Does have a pin on the rebound slide?

Very surprised about the 4/642 not having a hammer block. I’ll have to look into that. I’ll open mine up, it is the same vintage as your 442.

Well, looks like the wrong slide was installed.  Call S&W and they will send you a call tag I would imagine.

No, not mine in the pic. I don’t have a 638.

Yeah, check it and let me know.

From what I can tell the 638 definitely has a hammer block but I’ve never found any pictures where I could tell if the rebound slide had a pin.

I went ahead and ordered a rebound slide with a pin. I can’t see how that would hurt even if the 638 was supposed to be no pint.

I just had my new production 638, bought new in February, apart. It definitely has the pin for the block.
I also just worked on my 438, same gun only black, it too had the pin on the rebound.

Thanks for the info.  I went head and ordered a slide rebound with pin from Midwest Gun Works.  I know S&W would’ve taken care of it but this is likely quicker and easier.

So yes, my 642 has no hammer block and the slide is not drilled for the pin.  Have had 36 and 60 models in the past but never opened this 642 before (late 1997 vintage).

I guess that makes perfect sense as there is zero exposed hammer unlike the Bodyguard models.  Wonder if it was made that way accidentally, or repaired incorrectly by someone?  Seems it should have caused problems somewhere along the way before now.

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I’ve had it for probably a year and only have about 150 rounds through it.  It was definitely new when I bought it.

I’d disassembled once to do some simple polishing and remember thinking at the time it was odd how the hammer block was just loose in there.  

My best guess on why it hadn’t happened prior to now is-
1.) it’s had some shooting/carry time and has built up enough gunk internally to hold the block in the wrong place, and,
2.) When the FTFs occurred I was shooting nearly directly downwards.  

Previously, I’d been shooting (horizontally) at steel and targets.
I suppose it being clean and pointed horizontally gravity always kept the block out of the way.