SD Striker release

[ou1954]

This question relates to my SD9VE [CA for me] as I study how the various parts work. I now understand the whole process of loading rounds from the magazine, and the functions of the slide, the extractor, and the ejector.

What I can't quite understand is what causes the U-shaped piece*, [actuated by the trigger bar], to decide exactly when to release the striker after pulling it back from it's preset position. I see it moving rearward with trigger pull but it seems to be sliding down a smooth ramp with nothing else visible.

I see a protrusion on the trigger bar that pushes up the striker safety button, and, with the slide off, I can release that U-shaped piece which snaps forward. I also see, on the underside of the slide, a linear cam which could push down the protrusion, and thus the U-shaped piece, and release it, but it's pretty far from where it would have to be.

I can see, by looking under the slide back plate, that the U-shaped piece is pushed back by the trigger bar and can see that at some point, some magic happens which releases the striker.

What is that magic? I have seen reference to a "cam" in a post in this forum, and have searched the patents S&W links to the SD, and some earlier models, but no mention of a cam - mostly details and features of extractors, etc.

The Glock video animations show the striker being released but there is no detail on what releases it.

Does anyone understand just why the striker is released at the same point and what releases it?

*Some videos refer to this as the Sear, a common release part on other guns.

 

[brchambersjr]

The sear basically rotates slightly on its pin as it is pushed back by the trigger bar. If you take the slide off and look at the sear from the side, pull the trigger and you can see it make a small arc as it is pushed back and ultimately down.

Bill

 

[ou1954]

I have a California gun and the sear area has at least two additional parts and one more spring than the standard version. You can see, in the manual, one of the extra parts which is a magazine present sensor. If this is not pushed up by a magazine the trigger bar is not allowed to engage the sear. The instructions require you to pull the trigger while pressing that lever/sensor down before removing the slide.

The second part is a flat ramp bar that the sear rides on as the trigger is pulled. At some point magic happens and the sear drops down, releasing the striker, but I don't see any rotation of the sear.

The best simulation I can do is to remove the slide using the instructions in the manual. Then I insert the magazine which pushes up the magazine safety and allows the trigger bar to connect to the sear. Also, with the magazine in place, the "ramp" bar is raised and the sear slides along it when the trigger is pulled. If I do that and then push down on the rear prong on the trigger bar, the sear is released and pops forward.

With the gun assembled and the magazine in, I can peak under the slide rear cover and see the sear moving back as the trigger moves. At some point the sear pops loose, releasing the striker. I just can't see what causes the sear to be released.

If the magazine is out the trigger bar sits low and does not move the sear.

I do have the feeling that the linear cam lobe on the underside of the slide does hits the rear prong on the trigger bar but am not sure what that does.

A question for non-CA owners. Does the bottom of the slide have not only the striker blocker (looks like a round button) but also a linear cam (bump) further towards the rear of the slide, both in the grove where the trigger bar lives?

 

[ou1954]

Bill, Thanks

I do see that the sear does indeed rotate slightly forward when you release it by pushing down on the rear protrusion of the trigger bar. Exactly the behavior shown in an Apex video.

I just don't see what causes this action to occur when the trigger is pulled in an assembled gun. It just pops when the trigger reaches a certain point but there must be an invisible hand to push the trigger bar down.

 

[Muss Muggins]

Bill, Thanks

I do see that the sear does indeed rotate slightly forward when you release it by pushing down on the rear protrusion of the trigger bar. Exactly the behavior shown in an Apex video.

I just don't see what causes this action to occur when the trigger is pulled in an assembled gun. It just pops when the trigger reaches a certain point but there must be an invisible hand to push the trigger bar down.

In the Glock, as the trigger is pressed, the trigger bar draws the firing pin back, compressing the firing pin spring and preparing the weapon to fire. The frame and internals are designed so that the trigger bar drops off the firing pin after being retracted a certain distance (the "drop safety," the third safety in a Glock), releasing the firing pin. I can only assume the S&W functions similarly, as this is generally how striker fired pistols work. The firing pin is under little, if any, tension, pressing the trigger draws the pin back and prepares it to fire, and after a certain trigger travel distance, the firing pin spring is compressed, the firing pin is loaded, ready to fire, and the trigger bar drops off, allowing the firing pin to travel forward. This is why striker fired pistols won't go off in your pocket unless you press the trigger.

 

[ou1954]

Yes, I see that in the available Glock animations. In the SD series there is a striker blocker that is pushed up by a prong on the trigger bar. That's shown in an Apex video done by Scott Folk.

That striker blocker is a hollow cylinder held in by the extractor and Scott shows how to replace it's spring with an Apex spring which is one of the weaker springs they put in to reduce trigger pull.

I just don't/can't see what makes the sear decide when to release the striker.

Have you seen the Youtube video by Apex, the one that shows how to install their spring kit?

 

[ou1954]

Here is my slide showing the round striker blocker.

 

[brchambersjr]

As the sear is pushed back it is gradually pushing on the striker "lug" and sliding down at the same time due to the radius it is traveling caused by it's pin on the bottom. It only moves down about 1/8" and releases.

The bump causes the trigger bar to disconnect from the sear as the slide moves rearward.

Bill

 

[ou1954]

Thanks Bill,

I'm gradually getting the picture. My CA version has several more parts and springs in the sear block assembly, all related to the magazine safety feature.

These hide part of what's going on so I will try to have a look at one next time I get to Bass. I spent a lot of time in getting Bass to sell CA guns here in Oklahoma and developed a relationship with the gun department manager and assume he will let me open their display model.