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Discussion Starter #1 (Edited)
I don't think this has been posted anywhere, and I'm sure there are others out there who are like me in that they love knowing exactly how things work. So, I decided I would write a post detailing the internal mechanics of a Sig P229 DA/SA SRT pistol. This explanation will cover other DA/SA SRT pistols in the P-series, but I'm specifically using the P229 as a reference. Some of you will already know this, and some of you may not care, but hopefully this will be helpful (or at least interesting) to some of the readers on this forum. :) Enjoy!



When the firearm is at rest and decocked, the sear is held into the top notch of the hammer (the safety intercept notch) by sear spring tension, which blocks the hammer from being able to move forward to contact the firing pin (in case the firearm is dropped, for example). The rear arm of the trigger bar is sitting in the bottom notch (the double-action notch) of the hammer, and the safety lever is not engaged (thus, the firing pin is blocked).

When the trigger is pulled with the hammer decocked, the trigger bar moves forward, and the rear arm of the trigger bar pulls the hammer rearward by pressing on the front of the double-action notch, causing the pivoting motion. During this motion, the sear simply slides along the surface of the hammer. Right before the rear arm of the trigger bar pops free of the double-action notch, it makes contact with and pushes the long arm of the safety lever forward, which raises the tip of the safety lever and unblocks the firing pin. JUST before the sear reaches the middle notch (the single-action notch) of the hammer, the rear arm of the trigger bar pops free of the double action notch, and the hammer flies forward under the mainspring pressure. At the same time, the top arm of the trigger bar blocks the sear from moving backward and re-engaging the safety intercept notch by applying forward pressure to the sear arm. The hammer is no longer blocked, so it "slingshots" across the gap and slaps the firing pin, which fires the gun.

The rearward travel of the slide during recoil pushes the disconnector on the trigger bar down, which drops the top arm of the trigger bar down below the sear arm, allowing the sear to once again contact the hammer so that the saftey intercept notch will keep the hammer from accidentally hitting the firing pin. Even though the trigger bar is no longer exerting pressure on the sear, the rear arm of the trigger bar is still keeping pressure on the long arm of the safety lever, which keeps the firing pin unblocked. The slide continues backward and pushes the hammer back to the point where the sear engages the single action notch, and the hammer is thus cocked in single-action mode. As pressure is released on the trigger during trigger reset, the trigger bar spring pulls the trigger bar back and upward until the top arm of the trigger bar re-engages itself behind the sear arm. The "click" of the trigger resetting is actually the sound of the top arm of the trigger bar popping up behind the sear arm. This rearward movement of the trigger bar, however, is not enough to release pressure on the safety lever, so the firing pin remains unblocked. The Short Reset Trigger offers such a short reset because the firing pin block remains disengaged during the slide cycle, and the long trigger reset needed to re-actuate the safety lever (as seen on non-SRT pistols) is not needed. When the gun is fired from here, the trigger bar simply moves forward, pushing the sear arm forward and disengaging the sear from the hammer (and keeping the sear from engaging the safety intercept notch), so the hammer can strike the firing pin.

When the hammer is cocked by the user's thumb, the rear face of the double-action notch pushes the rear arm of the trigger bar forward (thus moving the trigger back), and at the same time, the hammer rotates until the sear engages the single-action notch. When pressure is applied to the trigger, the rear arm of the trigger bar moves forward and applies forward pressure to the safety lever, thus raising the tip of the safety lever and disengaging the firing pin block. The initial takeup you feel when squeezing the trigger for the first single action shot (i.e., "taking up the slack") is actually the process of disengaging the firing pin block. Finishing the trigger pull moves the trigger bar forward so that the top arm releases the sear from the single-action notch, keeping it out of the way so that the safety intercept notch is not engaged, and the hammer strikes the firing pin.

When the hammer is cocked and you press the decocking lever, the arm of the decocking lever simply pops the sear just out of engagement with the single-action notch of the hammer, thus releasing the hammer. The sear is not held away from the hammer, though, so it will still engage the safety intercept notch. At the same time, the arm of the decocking lever catches the edge of the hammer, thus placing the rest of the mainspring tension on the decocking lever. The user then slowly (or quickly) releases this tension by releasing pressure on the decocking lever. The sear rides along the surface of the hammer until it engages the safety intercept notch, and the hammer is fully (and safely) decocked.


And that, in a nutshell, is how a Sig Double-Action/Single-Action with a Short Reset Trigger works. :)
 

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The Mechanical Engineer in me thanks you so much! you kept me from having to completely rip my 229 apart to figure it out for myself.
 

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Thanks for the explanation. I'll need to read it a couple of times before it gets through my thick skull, but it's great to know it's out there!


Victor Chelf
Houston, TX
Sent from my iPad using Tapatalk HD
 

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Discussion Starter #9
I'm glad to know I'm not the only one out there who likes this stuff! Glad to help, guys.

Great info and nice avatar too
Thank you very much! It was just a quick smartphone picture I took during a cleaning session.
 

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This post is so damn cool. Reading this, with the blown up schematic on my Tekmat was like sitting in a classroom lecture. Thank you for finally getting the mechanics of the trigger and all it's accompaniment into my thickly lined skull. Very, very cool stuff that I should definitely know about my own firearms. Great post, thanks again.
 

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Discussion Starter #12
This post is so damn cool. Reading this, with the blown up schematic on my Tekmat was like sitting in a classroom lecture. Thank you for finally getting the mechanics of the trigger and all it's accompaniment into my thickly lined skull. Very, very cool stuff that I should definitely know about my own firearms. Great post, thanks again.
Glad you liked it! Remove your slide and pop the grips off your Sig sometime and look in on the right side while you play around with it (slowly squeeze the trigger, press the disconnector, manually cock it, etc.). It truly is a marvel of engineering!
 

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That took a large amount of forethought and is very well written !

Thank You !!
 

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LOL. Talk about resurrecting an old post. Cracks me up, because he's since changed his avatar to that goofy one with the slide flying off, but somebody commented on his avatar from before by saying they liked it, and he responded that it's "just a quick picture he took during a cleaning session" lol.

It IS a good post though
 
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