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Knoxp9090
I'm using the Silencerco .30 flash hider with the ASR QD mount. I apologize but my memory is a bit fuzzy on whether or not I ended up installing the taper adapter or not - I remember calling Sig and asking for one, since it wasn't included with my "pistol" when I bought it from Cabelas - but I can't remember if I actually needed it or not. I may have tightened/red loctited it directly to the tapered barrel since the flash hider doesn't need to be timed like the muzzle brake, and it bottomed out flush just fine. On the 5.56 barrel I didn't do anything yet since I found out the Omega is not rated for a 9" barrel. I may sell my 9" barrel and get a 11.5" (once they become available)so I don't void my warranty from Silencerco.
When they first came out at Cabelas - I called around to the stores that were closest to me until I found the "pistol" with the Sig Brace and two barrels. Had them hold it for me, and drove down to get it. I form 1 the lower and took the Arm Brace out of the folding stock knuckle since it accepts a standard AR tube and put a BCM collapsible stock on it.
I've done one carbine class with it and ran it hard using 5.56 and it ran flawlessly.

Here are some of the upgrades that I've done so far:
Geissle 3GS trigger
Magpul+ Rubber pistol grip
BCM Stock
BCM KAG
BCM Keymod Covers
Phase 5 bad lever - Yes it does fit perfectly, but it renders your AMBI mag catch almost unusable due to it's location. Though I was willing to make this trade-off since I've grown too used to being able to lock the bolt back with weak hand and leave primary on fire control during firing/loading/unloading.

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Great to know,  thanks for the details.  If you happen to remember I am certainly interested in knowing.

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I haven't really noticed significant blowback with either the MCX or MPX. I have been using a small can with a 4.5" barrel though, so that may have something to do with it. I did notice it was sending brass pretty damn far in the distance last time I had it out.

Quoted:
TheTaxMonkey
You're welcome - this is a lot of fun, its neat to have one of these, so far I havent had any buyers remorse...hopefully it stays that way!

Yes - I have seen Tims video on the Military Arms Channel (one of my favorite channels) I was literally going "no no no!" at the screen when he chose the Scorpion. I respect him alot but I heartily disagree with his choice. I have no doubt the Scorpion is great - but I think the MPX is a better platform to mod and improve. That gun is the closest we are going to get as far as an HK MP5 unless we are an SOT or in the Mil/LEO community. At least for me, I think I would rather have almost limitless modularity and deal with a little gas blowback than be stuck with the Scorpion "as is". Dont like the trigger? Too bad, so sad, and the list goes on and on.  Im not knocking the Scorpion (for those who have one) I'm just saying despite the possible issues of the MPX (charging handle scratches, gas blowback etc) I'm confident that if Sig doesnt effectively correct tthese issues, the aftermarket manufacturing community will. We've seen that happen with a lot of firearm designs in the past (SCAR, AR, AK etc) and its only benefitted us the consumers. If a design has a slight flaw etc, companies will pop up that will take an already great design and put the final finishing touches on it.

Pros/Cons of MCX:
Pro - Weight, lightest weight of all my guns, even with accessories installed.
Compatibility across other rifle patterns.
I definitely like MCX ability to reuse a lot of the parts/magazines that I currently have, being that I'm an AR nut. It definitely fit the purpose I had in mind when I wanted to find a rifle platform that would shoot 5.56 and shoot it well since that's primarily what I would be feeding it. I also wanted the ability to shoot quiet and take advantage of 300blk. However, since it wasn't going to be the primary caliber, I didnt want to buy a dedicated rifle chambered in 300blk since it would only be a part time caliber. I also wanted to avoid a DI gas system since I knew I wanted to buy a suppressor and shoot with minimal junk blowing back at me. I didn't know of any otther rifle than the MCX, that was piston and chambered in 300blk. I have two piston ARs from LMT but LMT does not make a piston drive 300blk barrel. If I wanted to shoot 300blk with my LMTs I would have to switch them back to DI definitely not preferred.


Cons -  The jury is still out on the front handguard/gas system on the rifle. I see now that Sig is issuing a non-self adjusting gas systems on their new rifles/pistols. I have noticed that the front of the rifle does get hot, and I have to be mindful of where I place my weak hand during sustained firing. I hope to take more classes with it to really see what is going to work and what isnt. I will be anxious to see if it devolops any issues with the non-adjustable gas system.
I wouldnt say this is necessarily a CON persay - but I hope Sig gets caught up with the accessory side of the house - the whole point of this new rifle is modularity, what is the point of having the ability to accept 5 different stock types if they arent available? I recognize this is temporary problem though.
Availability of keymod mounts that are usable on the MCX. This is a minor problem and is symptomatic of the aftermarket not caught up yet - but I've found that keymod mounts that work fine on an AR (BCM keymod rail for instance) dont work on the MCX because the handguard is different. I like the flashlight mounts that hugg the rail as close as possible - since most AR rails are octagon in shape, there is a place for the flashlight "to fit" at the 11 or 1 o'clock position. This is not the case with the MCX and I will have to come up with something different in order to mount a Surefire Scout in the same fashion as on my ARs.
These are the only cons I can think of at the moment - I honestly need to run it longer to see how things shake out over time

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Anyone have a line on who has the MCX pistols, preferably the kit, available?

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Shot the MCX yesterday!  It is so sweet it is beyond words.  This is my first pistion rifle and I enjoyed the difference. Accuracy is solid, like the sights, the weight is so balanced.  Rifle is 95% perfect.  Two things- 1 trigger is a brick.  I would guess 8.5lbs min.  2. There is a little upper play in the front pivot pin. If you have seen the rifle in person there is a gap at the rear that Sig managed with a spring detent under the rear pivot pin.  It goes exactly where an accu-wedge would be.  

Anyone else have any play in the front pivot pin?

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I may do the shims, thanks for the link.  On another note I had the Muzzle Break swapped last night.  My gunsmith said he was starting to wonder if he was going to be able to get the Sig one off.  He said the force needed to get it off was really significant.  He ended up using his heat gun to get it off.  He said he was really surprised but how effective the taper lock is. Swapped out the sig flash for the Specwar mount and it seemed to lock up fine on the taper, used a little extra rockset but only torqued to 20ftlbs.  Installed the can and checked for alignment down the barrel and all looks good.

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How does it compare to the 516? I know the 516 is heavier but what else is really different about the two? I have a 516 carbon ts and I love it but I am really itching for the MCX.

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Can anyone comment on the performance of the MCX in the 5.56 configuration?

I plan to keep it as is in 5.56, 16" barrel but as I understand the MCX was built around .300 and being a dedicated suppressed rifle. Just don't want to drop money on something that won't utilize its full potential.

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You say John Hollister has one of "our" 9"  300BO kit guns. Are you saying you work for Sig Sauer or are you talking about something not related to the MCX?

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Quick question,  what is the coating in the bolt now.  Before it looked it NickleBoron, classic silver appearance.  My MCX bolt has a darker finish, so I'm guessing a PVD or ion bond type?

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I have a question.

Do you know when the folding stock will be available for purchase?  I ordered mine in August.

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I've handled a MCX carbine twice now and am thinking of getting one for my next purchase.
One concern I have is how the front sight mounts on the handguard, which slides off the rifle.
Any zero issues?
Also, I've seen a vid where a guy was swapping barrels and he expressed concern over the durability of the way the barrel attaches.
Anyone care to chime in on this?