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Let’s see How to Disassemble and Reassemble a Sig P365 FCU Step-by-Step. Want to work on your P365 slide next? Check out our full slide disassembly guide here.
The Sig P365 fire control unit (FCU) is the heart of the pistol—and learning how to take it apart and put it back together is key for deep cleaning, Cerakote prep, or replacing internal parts. This guide walks through every step of a full FCU teardown and reassembly.
This applies to the standard P365, though much of it also carries over to the XL and X models. No upgrades needed—just solid, careful work and a few basic tools.
TL;DR – Sig P365 FCU Breakdown
Start by removing the slide catch, trigger bar spring, and disconnector
Remove the takedown safety and lever before moving to the trigger
Punches needed: 1/16″ and 3/32″
Reassembly is the reverse process with extra care around spring alignment
Full walkthrough and timing below
Video Index
00:26 – Removing the slide catch 00:47 – Removing the trigger bar spring 01:20 – Removing the disconnector 01:44 – Removing the safety lever 02:16 – Removing the takedown safety 02:55 – Removing the takedown lever 03:17 – Removing the trigger bar and trigger 04:21 – Removing the sear and sear spring 05:10 – Removing the receiver retention pin spring and slide catch lever spring 06:05 – Installing the receiver retention pin spring and slide catch lever spring 07:04 – Installing the sear and sear spring 09:38 – Installing the trigger bar and trigger 10:43 – Installing the takedown lever and takedown safety 11:48 – Installing the safety lever 12:31 – Installing the disconnector 13:07 – Installing the trigger bar spring 13:57 – Installing the slide catch
How Do You Remove the Slide Catch on a P365 FCU?
Grab the slide catch and pull upward to release it. It should come out easily from the left side of the FCU.
How Do You Remove the Trigger Bar Spring?
Use three fingers to brace the trigger and prevent movement. Then use a small screwdriver to lift the trigger bar spring from its notch. Slide it out gently—it’s small and easy to misplace.
How Do You Remove the Disconnector on the P365?
Lift the rear of the trigger bar up and away from the FCU. With the trigger bar out of the way, slide the disconnector out from behind it.
How Do You Remove the Safety Lever and Takedown Safety?
Push the pin on the left-hand side of the FCU just far enough to release the safety lever. Tip the FCU upside down and it will fall out.
Push that same pin a bit farther (but don’t remove it completely) to free the rear of the takedown safety. Then rotate the takedown lever rearward and remove the takedown safety.
How Do You Remove the Takedown Lever?
Rotate the takedown lever fully forward, then pull it straight out of the FCU.
How Do You Remove the Trigger and Trigger Bar?
Use a 1/16″ punch to remove the trigger pin from the right side. Pull the trigger bar slightly to disengage it from the knob at the back of the trigger, then rotate and remove it. Finally, push the trigger forward and remove it.
How Do You Remove the Sear Pins and Sear Assembly?
Use a 3/32″ punch to finish removing the safety lever pin. Then drive out the larger sear pin using the upper hole on the right side of the FCU. The sear and sear spring will fall free.
How Do You Remove the Slide Catch and Retention Springs?
Use a small screwdriver to lift the receiver retention pin spring off the rear right side. Then move to the front left of the FCU to remove the slide catch spring by prying the short leg out of its notch.
How Do You Reinstall the Receiver Retention and Slide Catch Springs?
Place the flat leg of the retention pin spring into its groove and rotate it into place on the rear right side. For the slide catch spring, insert the long leg into its rear-facing groove, compress with a screwdriver, and snap the short leg into position.
How Do You Reinstall the Sear, Spring, and Pins?
Hook the spring into the notch on the sear. Insert the sear into the FCU with the tab aligned in its slot. Use a 3/32″ punch to align the upper hole, insert the spring, and replace the punch with the sear pin.
Now move to the lower hole and insert a punch until it hits the short leg of the spring. Use a screwdriver to lift the leg so the punch can pass through. Replace it with the safety lever pin.
How Do You Reinstall the Trigger and Trigger Bar?
Insert the trigger into the FCU with the face forward. Install the trigger bar eye onto the knob on the back of the trigger. Rotate the bar into position, align the holes, and reinstall the trigger pin from the left side.
How Do You Reinstall the Takedown Lever and Safety?
Insert the takedown lever from the left, then rotate rearward. Insert the hooked end of the takedown safety into the FCU, then insert the ball end into the slot in the bottom of the lever. You’ll feel spring tension when it’s right.
How Do You Reinstall the Safety Lever?
Place the hooked end of the safety lever forward into the slot beside the sear. Align the hole with the lower hole in the FCU and use a 3/32″ punch to hold it in place. Then replace the punch with the safety pin.
How Do You Reinstall the Disconnector and Trigger Bar Spring?
Slide the disconnector into its groove in the FCU. Then wrap the trigger bar around the back of it.
Install the trigger bar spring by placing one leg through the hole in the FCU and catching the other side slot. Use a screwdriver or spanner bit to seat the other leg into the hole on the trigger bar.
How Do You Reinstall the Slide Catch?
Place the rounded end of the slide catch into the left-side recess of the FCU. The tab should align with the spring. Hold everything together and use a small screwdriver to seat the spring into the tab. Then press it into place.
Final Thoughts on the Sig P365 FCU Reassembly
This FCU is tighter and more compact than the P320’s, with more side-to-side part movement. Take your time, keep springs aligned, and don’t force anything.
If you found this helpful, check out more P365 content on the site—and keep an eye out for our upcoming tools breakdown for FCU work.
FAQ – Sig P365 FCU Maintenance
What punch sizes do I need for the P365 FCU? You’ll need a 1/16″ punch for the trigger pin and a 3/32″ punch for the sear and safety pins.
Is the Sig P365 FCU serialized? Yes. The FCU is the serialized component of the P365 and considered the actual firearm by the ATF.
Can I swap the P365 FCU into a different grip module? Yes, that’s one of the benefits. You can move the FCU between different grip modules and slides as long as they’re P365 compatible.
Is the P365 FCU the same as the P365 XL? Mostly. The core components are the same, but things like the trigger shoe and lever may vary slightly depending on the model.
Do I need to replace the springs when doing a teardown? Not unless they’re damaged or worn. Inspect for bends, cracks, or soft tension. Replace if anything seems off.
Visual guide for disassembling and reassembling the Sig P365 FCU – Watch the full teardown
Original Content by The Rogue Banshee / My Rogue Solutions LLC. Credit: Jason Schaller Email: [email protected]
About the Author: Jason Schaller is a former FFL holder and founder of Eagle Eye Shooters Supply in Helena, MT, where he provided professional gunsmithing services and guided customers on all aspects of firearms ownership. Today, he teaches DIY gunsmithing at The Rogue Banshee and serves as a Chief Instructor at Freedom Crew University. With over a decade of hands-on professional experience with firearms and nearly 30 years in IT, Jason also holds top cybersecurity certifications including CISSP, CISA, and CRISC. When he’s not geeking out, he’s helping others build self-reliance, critical thinking, and firearms proficiency through real-world content.
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