4516 Part failure...super light single action shots

[Tfrag]

DA trigger pull is normal, but follow up single action shots are too light, almost unpredictable hair trigger feel. It’s a ‘no dash’ and I have a full spring kit enroute. What else should I look at? Trigger and sear, but not sure how to assess them for wear...

Lots of parts in these old beauties!

[S&W59]

There's actually not as many parts as you might expect. The trigger, trigger bar, disconnector, sear, and hammer are the main components with the three 'arms' near the hammer controlling the firing pin safety, magazine safety, and sear arm. I suspect the culprit here is the sear's interaction with the single action hook on the hammer. If I were the owner, I would detail strip the action, allowing the hammer, sear, and disconnector to drop free and be cleaned. You can also inspect the sear spring on the frame to ensure its not broken. There are a few how-to's on YouTube on how to disassemble and reassemble the sear/hammer/disconnector. Its maddening at times to put it back together, but after a few times, its second nature.

You also have the option of sending the pistol back to Smith and Wesson for them to address the issue for you. It could likely be a lifetime warranty issue but even if not, the fee wouldn't be prohibitive.

[BMCM]

Is this a gun that's new to you? Or...a piece you've owned for some time that has recently started acting up?

Without examining the guts firsthand, it's hard to definitively say what the cause of your problem is.

However there are three things I would suspect at fault for a dangerously light SA pull. Aftermarket mainspring especially a reduced power spring. Worn or modified sear, worn or modified SA hammer notch. Any one of those alone or a combination thereof can be at fault. In evaluating the hammer, of the three notches, the notch closest to the strikeface is the SA notch. The middle notch is the pickup notch, and furthest from the strikeface is the throw notch. Only the SA notch interfaces with the sear. The pickup & throw notches only engage with the drawbar.

I kind of surmise from your post you have already taken the gun apart so...

In this thread M1006 - Fixing bad action job I posted some pics that might help you in evaluating the condition of your hammer & sear.

And... I strongly recommend nothing other than the factory S&W mainspring which is part number 069740000 and in stock at Midway.

Cheers
Bill