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MCX with New Carriage Assembly Finally Passes!!

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Yep, I'm finally happy with my MCX's new Carriage Assembly!! After 2 February trips to Exeter, a new Upper, plus installing POF's Roller Cam Pin - She ran 90rds of mixed Federal & PMC 5.56 and .223 ammo today - Perfectly!!

We have vertually NO cam path wear, and only a slight line in the alloy finish inside the upper where the Firing Pin Retaining head rubs.

Her bolt locked back on every empty mag for a variety of Magpul and Lancers too.

Here's the Upper's cam path with only SIG's test fire and my manual cycling.



Here's the same Upper's cam path after 90 rounds today.



Here's couple shots of POF's clever Roller Cam Pin's installed. This little trick provides a noticeably smoother action in both this MCX and my SIG516s.





She's not perfect though. The Firing Pin Retaining pin sticks out just enough to make this line mark in the Receiver's finish.



And wears the finish off a small spot on the head of this Retaining pin.



I mentioned my 2 Exeter trips for this rifle's Carriage Assembly recall to our range officers today. They said they've heard that a lot - 2 trips seemed pretty standard. But, I think we're now good to go!!

Cheers

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Discussion Starter · #3 ·
You're right Mr Adiboo - Thanks!!

I'll admit that when you mentioned a POF roller cam pin may help, I had no idea what that was. Yeah, this is yet another example of my ST learning experience, where even a pretty slow chap like myself can occasionally find an acorn!!

Here's POF's Roller Cam Pin for my 308 that arrived yesterday



Cheers
 

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I disassembled my MCX for a detailed cleaning for the first time (with special focus on the new BCG) since buying it last year. I should have snapped a pic! Wow. There sure are a LOT of parts! Oh and it's amazing how much oil Sig slaps on these rifles.
 

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Discussion Starter · #5 ·
I disassembled my MCX for a detailed cleaning for the first time (with special focus on the new BCG) since buying it last year. I should have snapped a pic! Wow. There sure are a LOT of parts! Oh and it's amazing how much oil Sig slaps on these rifles.
Yeah, I was cleaning today too. She runs very clean, but there are a bunch of parts here!! We gotta be very careful if we have different barrels gas systems broken down at the same time.

I had a 16" 5.56 and the 9" 300Blk taken down on my bench, and noticed their gas valves are super easy to switch to the wrong barrel. They look almost exactly alike - the same size, same little ears, you have to look VERY closely to tell them apart.

There're only slightly larger ports on the 9" 300's valve, and different codes stamped into each sleeves.

My 16" 5.56's valve has 'C01', and the 9" 300Blk has 'F02'.

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Congrats on finally having a running MCX! If I could ask for your advice? Since getting my "upgraded" BCG, the bolt no longer locks to the rear on an empty mag (haven't taken it to the range yet, not sure if I should with a known malfunction). Actually that's not true, on USGI mags I can get it to lock back about 1 out of 10 tries, no dice with other brands (which used to work fine). Sig CS tried to blame it on MAGPUL, which was a little insulting. Anyway, do you think the POF Roller Cam Pin will help? I'm seeing the same little bit of wear on the firing pin retaining pin, but haven't yet noticed the cam pin wearing into the receiver but as I said, haven't been to the range yet. FWIW I too would rather spend $25 and "fix it myself" than go through multiple trips to Exeter as you went through! Thanks in advance!
 

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Congrats on finally having a running MCX! If I could ask for your advice? Since getting my "upgraded" BCG, the bolt no longer locks to the rear on an empty mag (haven't taken it to the range yet, not sure if I should with a known malfunction). Actually that's not true, on USGI mags I can get it to lock back about 1 out of 10 tries, no dice with other brands (which used to work fine). Sig CS tried to blame it on MAGPUL, which was a little insulting. Anyway, do you think the POF Roller Cam Pin will help? I'm seeing the same little bit of wear on the firing pin retaining pin, but haven't yet noticed the cam pin wearing into the receiver but as I said, haven't been to the range yet. FWIW I too would rather spend $25 and "fix it myself" than go through multiple trips to Exeter as you went through! Thanks in advance!
I had issues with my MCX Gen2 BCG locking back on an empty Pmag after manual cycling. I posted a few times on the forum about it (search for them). My MCX ran and locked back perfect before the recall. I sent the BCG in and received a new one. Shot 100 rounds through it and noticed the issue with the PMags. However, Lancers locked back perfect after shooting or manual cycling. Called SIG and requested a replacement in early February and it finally shipped yesterday. It will take another week. During this time, I tried the POF roller cam pin but it didn't solve it. From what I can gather, the bolt or assembly are out of spec. The bolt face was resting on the PMag follower, preventing the bolt catch from engaging. The Lancers have a different follower and allows clearance for the bolt face. Try slowly manual cycling the bolt on an empty Pmag and you will see. If this new BCG doesn't work, they said I will need to send the rifle in. Like you, I also wanted to fix it instead of sending it in.
 

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Congrats on finally having a running MCX! If I could ask for your advice? Since getting my "upgraded" BCG, the bolt no longer locks to the rear on an empty mag (haven't taken it to the range yet, not sure if I should with a known malfunction). Actually that's not true, on USGI mags I can get it to lock back about 1 out of 10 tries, no dice with other brands (which used to work fine). Sig CS tried to blame it on MAGPUL, which was a little insulting. Anyway, do you think the POF Roller Cam Pin will help? I'm seeing the same little bit of wear on the firing pin retaining pin, but haven't yet noticed the cam pin wearing into the receiver but as I said, haven't been to the range yet. FWIW I too would rather spend $25 and "fix it myself" than go through multiple trips to Exeter as you went through! Thanks in advance!
PMAG2s don't lock the bolt back on my new MCX BCG from SIG. PMAG3s lock the bolt back on my last round, but the bolt will drop as I remove the mag unless I keep my thumb on the bottom of the bolt lock/release lever.

Bill
 

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Discussion Starter · #15 · (Edited)
MCX Bolt Catch Failures

Hmm - Looks like we gotta bunch of Bolt Catch failures here??!!##..

Seems to me that these failures on simply inserting an empty mag, and the bolt doesn't lock back with a manual charging handle pull may be easier to diagnose than bolt lock failures after a mag's last round.

I mean, this is a very simple action where the charging handle pull MUST move the bolt rearward to a position ~1/8th" behind bolt catch's flat vertical edge. The mag's follower will then press up on the bolt catch's forward extension to position the bolt catch in front of the bolt - and thus locking the bolt back. TAa-DAa!!

Here's a pic with the bolt's breech face on the left, the bolt catch's vertical edge in position to lock back the bolt, and the bolt catch's forward extension held up on the mag's follower in the pic's center.



I'm guessing that these lock back failures may be caused when the charging handle's pull doesn't move the bolt far enough rearward for the bolt to move past the bolt catch's vertical edge. This 'short-stroking' bolt would not allow the bolt catch to move up, even with a mag follower pushing up on the bolt catch's forward extension.

This rearward bolt action's limitation could very well be an out of spec Carriage Assembly by simply not allowing the bolt to move far enough back. If so, while a roller cam pin may help with receiver gouging, it probably wouldn't have any effect on these bolt lock back failures. Just one man's theory...

Cheers
 

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Hmm - Looks like we gotta bunch of Bolt Catch failures here??!!##..

Seems to me that these failures on simply inserting an empty mag, and the bolt doesn't lock back with a manual charging handle pull may be easier to diagnose than bolt lock failures after a mag's last round.

I mean, this is a very simple action where the charging handle pull MUST move the bolt rearward to a position ~1/8th" behind bolt catch's flat vertical edge. The mag's follower will then press up on the bolt catch's forward extension to position the bolt catch in front of the bolt - and thus locking the bolt back. TAa-DAa!!

Here's a pic with the bolt's breech face on the left, the bolt catch's vertical edge in position to lock back the bolt, and the bolt catch's forward extension held up on the mag's follower in the pic's center.



I'm guessing that these lock back failures may be caused when the charging handle's pull doesn't move the bolt far enough rearward for the bolt to move past the bolt catch's vertical edge. This 'short-stroking' bolt would not allow the bolt catch to move up, even with a mag follower pushing up on the bolt catch's forward extension.

This rearward bolt action's limitation could very well be an out of spec Carriage Assembly by simply not allowing the bolt to move far enough back. If so, while a roller cam pin may help with receiver gouging, it probably wouldn't have any effect on these bolt lock back failures. Just one man's theory...

Cheers
You make some good points. My bolt breech face doesn't look like that when I lock it back. The bolt lock actually engages the assembly body and not the bolt face. Does yours engage the face?
 

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Discussion Starter · #17 ·
Yeah, with the charging handle fully back, the bolt's breech face is 1/8" behind the bolt catch, which the mag follower lifts up in front of the breech face to securely lock the bolt back.

Sounds like ypur bolt isn't moving far enough back for the bolt catch to properly deploy. Hope the new carriage assembly works for ya...

Cheers
 

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I just ordered a MCX that is due to come in this week. I'm concerned about all these BCG failures. I haven't found anyone posting good comments about the recall. Has Sig's QC gone down the drain? Seems all these issues could have been prevented with some good testing and fielding.

I've carried Sig pistols for the last 17 years and had few issues (mainly related to operating in a Marine environment). I hope my new MCX isn't just a paperweight. I sold my tricked out DI AR to get the MCX.
 

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FWIW, I ultimately decided to send my MCX in. Talked with Sig CS three times, explained the bolt failing to lock to the rear AFTER the new BCG installation, they insisted the whole weapon needed to go back. Anyway, about a three week process, rifle came back today. Their fix? A new buffer installed in the lower receiver. The original was an orange, rubber "doughnut" if I remember correctly? The new one is a tan colored, flat disc and looks quite a bit less substantial. Hope to hit the range tomorrow, curious to see how this all works out. Will report back, with pics I hope.
 

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FWIW, I ultimately decided to send my MCX in. Talked with Sig CS three times, explained the bolt failing to lock to the rear AFTER the new BCG installation, they insisted the whole weapon needed to go back. Anyway, about a three week process, rifle came back today. Their fix? A new buffer installed in the lower receiver. The original was an orange, rubber "doughnut" if I remember correctly? The new one is a tan colored, flat disc and looks quite a bit less substantial. Hope to hit the range tomorrow, curious to see how this all works out. Will report back, with pics I hope.
That's interesting. Very curious to see the pics.
 
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