P320 FCU Polishing / Trigger Job Discussion Thread - SIG Talk
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P320 FCU Polishing / Trigger Job Discussion Thread

This is a discussion on P320 FCU Polishing / Trigger Job Discussion Thread within the P250 & P320 Modular Pistols forums, part of the SIG Sauer Pistols category; I searched and didn't come up with a whole lot. If I am wrong, please let me know! I was recently brave enough to break ...


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P250 & P320 Modular Pistols P250, P320, and Exchange kits

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Old 01-05-2017, 10:53 AM   #1
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P320 FCU Polishing / Trigger Job Discussion Thread

I searched and didn't come up with a whole lot. If I am wrong, please let me know!

I was recently brave enough to break my FCU down to individual pieces which gave me a chance to look a little closer at the action and mechanism.

Most people know that the majority of the parts in the FCU are MIM (metal injection molding). The sear area and related components appear to be electro polished but surely not hand polished. There are a few locations that can really benefit from a solid polishing IMO.

I followed this video,
including the Mothers Mag polish and qtips. I found that the qtips worked best for the sear parts but a scotchbrite green pad worked very well for the outer surface of the FCU and trigger bar locations.

The polishing is rather laborious. It took me nearly 2 hours the first time and I ended up going back and doing some more after. It seems like the polishing takes a lot of effort to get any sort of finish and then all of a sudden it's nice and shiny (which makes sense if you consider exactly what we're doing).

I got pretty decent qualitative results. The action sure seems smoother and crisper with less "creaking" when pulling slowly. I'm not sure it actually reduced the overall force a ton but it's surely even smoother.

What I don't have the balls to do is remove one of the sear springs to try lightening the pull further.

Anyone else trying to be a mini-Bruce Gray?
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Old 01-05-2017, 11:24 AM   #2
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I think a dremel with a soft polishing bit will speed things up and be more effective.


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Old 01-05-2017, 05:09 PM   #3
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I took the sear apart once, and Ill never do it again.
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Old 01-05-2017, 06:25 PM   #4
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I've done extensive polishing on my FCU. I used 1000 & 2000 grit sand paper. My compact model breaks at 4.5lbs.
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Old 01-06-2017, 05:02 AM   #5
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Just shoot it. Every piece will wear perfectly.
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Old 01-06-2017, 05:38 AM   #6
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Wondering.......if MIM parts are a reliability issue......are there any machinists out there producing those same parts from stainless?
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Old 01-06-2017, 06:02 AM   #7
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Wondering.......if MIM parts are a reliability issue......are there any machinists out there producing those same parts from stainless?
In my experience with MIM parts, these seems to be not only of high quality but also very well designed for the MIM manufacturing process. I don't think there are any inherent reliability issues with any of these MIM parts.
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Old 01-06-2017, 06:31 AM   #8
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Your a brave soul. If I tried that it would be like an old 4 barrel carburetor job, I would have extra parts leftover.
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Old 01-06-2017, 06:35 AM   #9
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In my experience with MIM parts, these seems to be not only of high quality but also very well designed for the MIM manufacturing process. I don't think there are any inherent reliability issues with any of these MIM parts.
Ageed!

I am a bit suspicious of the suitability of the P938 extractor, however. We hear so many instances of the claw being broken. These could very well be broken by slamming the slide closed with a round in the chamber, but I see several cases, my incident included, in which I am confident chambered round slide slamming had not occurred.
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Old 01-06-2017, 07:40 AM   #10
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Not sure if applicable, but my smoothest SIGs are my Mastershop X5s and this CPO (used!) P226 in .40 S&W sans rails. My smoothest Glock is a likewise an unmodified, used 17L I got off Goonbrokaw.

The trigger feel should get better with use, I suspect.

Shoot it more frequently
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Old 01-06-2017, 07:49 AM   #11
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Not sure if applicable, but my smoothest SIGs are my Mastershop X5s and this CPO (used!) P226 in .40 S&W sans rails. My smoothest Glock is a likewise an unmodified, used 17L I got off Goonbrokaw.

The trigger feel should get better with use, I suspect.

Shoot it more frequently
Just put >600 rounds through it yesterday afternoon in various configurations. Got it nice and dirty and I'm gonna spend some time dry firing before cleaning again. Natural polishing compound.
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Old 01-09-2017, 05:59 PM   #12
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I just used your video this weekend and did a quicky polish while in there installing an Apex trigger and learning the FCU internals. I used a dremel with a cloth polishing wheel and the Ryobi SS polishing compound (From Home Depot). I started at 7.5lb + and ended with 6-6.5lb. I may go in for more later after I make sure I didn't dork anything up this go around after a range trip/test.

Thanks for the post and the vid!
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Last edited by KillerMedic; 01-09-2017 at 06:07 PM. Reason: fat finger typing
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Old 01-12-2017, 04:53 PM   #13
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Quote:
Originally Posted by KillerMedic View Post
I just used your video this weekend and did a quicky polish while in there installing an Apex trigger and learning the FCU internals. I used a dremel with a cloth polishing wheel and the Ryobi SS polishing compound (From Home Depot). I started at 7.5lb + and ended with 6-6.5lb. I may go in for more later after I make sure I didn't dork anything up this go around after a range trip/test.

Thanks for the post and the vid!
I took your advice and did what you did with great results. A little Mothers is just what the Doctor ordered.
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Old 01-16-2017, 04:26 AM   #14
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Anyone have a new link? That one seems dead.
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Old 01-16-2017, 01:16 PM   #15
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Anyone have a new link? That one seems dead.
Link for the OP's video? If so I just clicked it and it worked.
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