Mr. Glockbake's extensive firing of the MCX upper on a regular AR lower, suppressed, without the Sig conversion piece, without the MCX buffer to stop rear travel of the bolt carrier (leaving the recoil spring cup to do that job), or adequate support for the recoil spring assembly, had absolutely nothing to do with the failure of the recoil spring assembly in precisely the area that was not adequately supported. Purely Sig's fault.
Note 25:25 to 27:10, and various other spots in this video.

Good eye.  I figured that he would have screwed it up in some way before it failed like that.  It looks like the inside of the retainer plate is a little chewed up.  I wonder if he tried to smash the spring guide in there backwards a time or two before reassembly.  "Make it out of aluminum, because metal!" people seem to be the same that don't trust PMags "Because plastic!".  In his hands, it doesn't matter if it was made out of an alloy of adamantium and mithril, because he'd screw it up anyways.

I don't get the folks who are being overly critical of Sig for this.  Unreported in the field and extremely difficult to replicate in the lab.  I do think that they could have had better execution on the upgrade program with regards to the training of their customer service reps and their estimated timelines.  

I'm inclined to believe that the UK Metropolitan police and others who have adopted this platform have done a significant amount of testing on it.  I don't think that if there were serious flaws with the weapons system that Sig could get them to buy it.  Everyone keeps on saying "QC", when they don't realize that it's not a QC issue.  The accuracy issues were a QC problem.  This is a redesign.  Even Glock and FN, among other very reputable manufacturers, has had recalls and upgrades to otherwise fantastically reliable weapons.

WHAT HE SAID!

If you're going to shoot it like this:


You can see the poor little plastic part squeezing out the back with no support whatsoever!  I can see the argument for Aluminum over plastic-- Better yet Mithril / Adamantium / Unobtainium  -- Its like the part was not designed for that use.... Best argument ever to just use the god damn conversion piece!

Note the rather large upper support block:


Give him some more youtube hits ($$$):

Vid at time 27:08

What a joke!

I hope Sig comes through this time on parts for the MCX. That being said  I have a Sig 556R, Sig 551A1 and a Sig 556 Swat. When I tried to order parts for each and they were still being made all I got was "parts are not available right now but will be soon. Empty words. I was never able to get any of the spare parts I was told would be available later. Now Sig does not sell spare parts for any of these rifles and no longer supports any of them. Hope the MCX is not headed that way.

I'm in the same boat with my 556R. Can't get parts. It stays in the safe. I'll just sell it eventually.

I really want to like the MCX/MPX; but if I can't get parts I'm not investing in them.

If I was a betting man, I would say the MCX and MPX line are here to stay. Parts will eventually be available. I have both the MCX and MPX and they are by far the best and coolest weapons I have ever owned and I have owned many.

Hopefully once this recall/replace of BCG takes place, parts will open up some.   I am sure that was a huge bottleneck

I wouldn't doubt that they will be around for a while but who knows how many different generations they will come up with and stop supporting.

That is what they have done on their pervious rifles. I'll bet they will announce later this year another model. That gives them another rifle to drop and not support.

How are the replacement carriers working for those who've taken part in the recall?

No issues here.

No functioning problems with mine.

Has anyone here actually had a slam fire with their MCX. I'm really debating weather to send mine back or not. I think the whole thing is way overblown.  The new BCG will only add more Sig only parts that could fail later and we won't be able to get replacement parts.

I haven't seen the replacement carrier but I'll bet the firing pin lock could be removed if need be so a legacy firing pin could be used.

I've wondering about that. 
From the videos I've seen it looks like it's a pin that holds it and the spring assembly together. Wondering if simply leaving the firing pin block out will work?

The firing pin is retained via the firing pin retaining pin which is captive. The firing pin safety is held in via a separate pin, for that alone. The tension for the firing pin safety is from a spring loaded tab which has nothing to do with the firing pin and it's retaining pin.