I have a 5900 series S&W that the hammer follows the slide into battery when the trigger is not squeezed and the magazine release is used. In other words, when the slide is locked back and I release the slide with the magazine release lever, the slide slams forward and the hammer follows it to a decocked position. It will not do this when the trigger is squeezed (Thank God) and the firing pin block is preventing slam fires as a result. I am suspecting its either the sear or the sear spring. Before I put my order in with Numrich for both, is there anything else I should check or order, such as the sear release arm or disconnector?

I'm going to guess that you mean the hammer follows the slide when you depress the slide stop lever to release the slide to go forward? Not the magazine release. (The magazine release is not involved with the slide.)


Are you saying that if you pull the trigger on a live round, with the hammer cocked in single action, the hammer goes forward, the gun fires, the slide cycles and the hammer ... what? It goes forward, but the gun doesn't fire? It stays cocked in single action? I'm unsure what you're trying to describe.

Without being able to inspect the gun I can't pretend to know what's happening with your gun.

The usual probable causes of the hammer not holding in single action are:
Defective hammer (notches)
Defective sear spring (curled, split up middle or otherwise damaged so it won't hold the hammer)
Worn sear (nose points)
Drawbar binds

All of the above probable causes of the problem require replacement of the affected part, or parts.

That said, has the frame been disassembled recently? Is the top of the sear spring located against (behind) the rear of the sear's tail? In other words, the sear leaf spring must be pushing forward against the bottom of the sear, so the top of the sear is pushed backward to catch and hold the hammer's single action notches. Or, is it on the wrong side of the sear's tail (not providing proper tension in the right direction)?

Also, there are 3 types of sear springs that have been used over the years.

The current revision has a short raised center "ridge" running vertically, over which the sear spring pin rests.

The previous spring to that one had a pair of raised dimples in which the pin was centered.

The raised ridge better held the spring from shifting (even though the spring's tail was located in a frame hole, it had a little possible movement). The raised ridge also makes it a bit trickier to replace the spring, as the leading edge of the pin has to be pressed "inward" as its being installed, down (meaning forward, toward the back of the frame) and over the front of the pin, to align the pin with the opposite pin hole in the frame. A press was used at the factory, while armorers had to learn how to use a wide punch to find a way to push against the front of the pin, bringing it down/forward to meet the pin hole, while at the same time pushing the pin forward into the next pin hole.

Now, if it's a sear, hammer and/or a drawbar problem? While none of those are fitted parts, an armorer (or smith) still needs to know how to perform the usual bench checks to make sure the specific parts work as intended in a particular gun ("rocking" and holding the hammer in DA, no skips-DA, the pickup & notches of the hammer and drawbar align, the sear nose points hold the hammer in single action with light push-off, etc).

It might be a good idea to call the factory and ask if you could have the gun returned for inspection for a hammer-follows condition, as that's obviously a safety issue. Might not be a defect, but just wear over time, so they may not consider it a "warranty" issue (especially if you're not the first owner), and ant your credit card to bill you for the repair. Dunno. Can't hurt to ask, though.

Now that these guns have been discontinued and are considered "obsolete", parts seem to have become a bit harder to find, and can be pricey. When these guns were still in production, a new drawbar was almost $60 (retail), a sear (MIM) $25 and a hammer $42. The sear spring was cheap at $0.72.

Nowadays there's a market for used 3rd gen parts, it seems, so you never know what you're getting until it arrives.

Got a local gunsmith familiar with the 3rd gen guns?

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Ret LE Firearms inst & armorer

Fastbolt....the OP posted in two different locations. Here's some addn information found about this on the "Semi-Auto's" duplicate thread:

5900 series hammer issues.

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Ret. LE, FA Instr, S&W Armorer

Thanks.

While I suppose it's possible that some previous owner might've discovered a decocking problem and installed one of the older really over-long sear release levers (not knowing it needed to be filed/fitted), and it might (?) be so long that it might interfere with the sear while it was trying to hold the hammer at SA during cycling ... I'd still really want to examine the rest of the parts that can normally be involved when a hammer won't hold in SA.

Also, as you know, adjusting the "timing" of the decocking (hammer fall) is critical for safety. That's why the company finally started having armorers use the 3 differently sized metal drill bit shanks as 'gauges' to more precisely check the timing as the lever foot is filed (apparently because eye-balling it wasn't easily learned and similarly done by basic armorer students).

Ditto for it being critical preventing the hammer from following the slide forward. If someone deliberately (trigger 'reset' crowd) or unintentionally holds the trigger to the rear when the hammer follows the slide forward, or just doesn't release the trigger quickly enough, and the drawbar is lifting the firing pin safety lever, that means it's lifted and disengaged the firing pin safety plunger from blocking the firing pin. Not good. Having a 'runaway' firing cycle occur is extremely dangerous.

OP, if you're still reading this thread, STOP shooting the gun until someone who knows how to diagnose the cause(s) of the problem, and knows how to repair it, can correct the problem.

Calling the factory is a good place to start.

Just my thoughts. I'm outta this one ...

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Ret LE Firearms inst & armorer