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Sig MCX is .223, not 5.56 NATO

This is a discussion on Sig MCX is .223, not 5.56 NATO within the SIG Sauer Rifles forums, part of the SIG Sauer Forum category; I am frustrated as hell so I wanted to post this here and see if anyone else has had similar results. You know how it ...

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Old 11-24-2016, 05:50 PM   #1
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Sig MCX is .223, not 5.56 NATO

I am frustrated as hell so I wanted to post this here and see if anyone else has had similar results.

You know how it is. I told my wife I wanted to stop by a gun store just to see if they had a particular gun I wanted to look at and under no circumstances was I going to buy anything (I wanted to see if they had a Sig MCX in 5.56). Well low and behold they had one and I walked out with it much to my wifes disappointment. I picked it up about a month ago and have experienced nothing but disappointment.

The next day I bought a 420 round can of Federal XM193 55g 5.56x45mm and headed to the local range. Much to my disappointment, I was shooting 6-10" groups at 50m using iron sights. I mounted an Elcan Specter DR optic and shot 6-10" groups. I went home frustrated, mounted an extra EoTech XPS2 and 3x magnifier. Went to the range the next day and once again shot 6-10" groups. I walked over to the guy next to me and invited him to shoot my rifle to which he was more than happy to assist. He scored 2 of 3 rounds on paper with about a 4" group between the two impacts on paper. We tried 3 of his reloads and had similar results.

The next weekend I took some .223 to the range just to see how that went. I had Fiocchi 55gr .223 and G2 62gr .223. At the range, both ammunition shot 1" groups in the Sig MCX.

I bought an IWI Tavor X95 recently (and gave it to my wife because my wife was ****** I bought the Sig) and zeroed it at the range using the same XM193 ammo and shot sub MOA groups at 50m. This told me that there is no issue with the Federal XM193 ammunition I was using in the Sig that produced miserable results.

I emailed Sig:
"I spoke to you on the phone last week regarding my Sig MCX shooting 6-10" groups at 50m using Federal 5.56x45mm 55gr XM193. I have tried several different troubleshooting procedures including utilizing different optics (Elcan Specter DR, EOTech w/3xmagnifier and iron sights), 3 different shooters and 2 different types of ammunition all with similar results.
Before sending the rifle back to Sig, I decided I should go back the range and triple check my results. Attached is a PDF file of my range results shooting 3 different types of ammunition in the Sig MCX with Harris bipod and EOTech w/ 3x magnifier at 50m. The first image is my group at 50m using the Federal XM193. The second image is my results using Fiocchi .223 55gr. The third image is the results using G2 RIP .223 65gr. You'll see that the groups using .223 were much better than the first group using 5.56. The groups I achieved today with the 5.56 are similar to the groups I have shot in the past and are repeatable every time I shoot using XM193. It is obvious that this is not a manufacturer flaw with the weapon. The weapon does not seem to like Federal XM193. My next task will be to buy some XM855 or other 5.56x45mm that is a different manufacturer and/or different grain and see if I get similar results as I did with the XM193"

Sig Replies:
"I spoke with a few people on their thoughts regarding your situation. With the XM193 your accuracy should be around 3-3.5 MOA but it can vary between brands. The superb accuracy with .223 is not uncommon for a barrel chambered in 5.56, there are many variables that come into play with the bullet type, load and overall design of the round itself that will dictate the achievable accuracy of the rifle. I think in your case with the specific 5.56 you tried gave you poor results and this might change with different 5.56, If you are looking for the same results every time that you got with the .223 I would use those exclusively. At this time if you send the rifle in we can still test for accuracy, but It would seem that your barrel is ok, and you may have received some surplus 5.56 that gave you some off groupings. Let me know your thoughts and how you would like to proceed."

This didn't make sense because I was shooting .5-1 MOA groups with the Tavor. So I bought a box of American Eagle XM855 62gr 5.56 and headed to the range. The email I sent to Sig will explain everything:

Email to Sig:
"I conducted some more tests this week. I used 2 rifles, the Sig MCX and my wifes IWI Tavor X95. Both rifles have a 1:7 twist and claim to be chambered for 5.56 NATO (5.56 NATO is stamped in the barrel of the X95 and MCX) as well as both having a 16.5" barrel. The Sig MCX had an EoTech XPS with EoTech 3x magnifier. The Tavor X95 had an Aimpoint CompM4 with EoTech 3x Magnifier. Both rifles had a Harris bipod.
I brought Federal XM193 55gr 5.56x45mm and American Eagle XM855 62gr 5.56x45mm. I shot a group with the Sig MCX using XM193 that resulted in a 9.5" (4.75 MOA) group at 50m depicted in image#1 attached. I then loaded XM855 and shot 3 rounds in the same conditions that resulted in a 2" (1 MOA) group seen in image#2 attached. Utilizing the same XM193 and XM855 ammunition, I shot the IWI Tavor (zeroed for my wife to which I shoot high left). Both XM193 and XM855 resulted in 1" (.5 MOA) groups at 50m seen in image#3 attached. Now i have verified that the ammunition is not an issue. I reloaded the Sig MCX with XM855 and shot 2 more groups which resulted in a 4" (2 MOA) group and a 2" (1 MOA) group seen in the top right then top left respectively of image#4. Images 5 and 6 were from last week when I fired Fiocchi 55gr .223 and G2 62gr .223 through the Sig MCX that resulted in .5 MOA groups.

The Tavor X95 is shooting sub MOA groups using the same 5.56 XM193 and XM855 so the ammunition is not defective. The Sig MCX is shooting sub MOA groups utilizing .223 but I cannot shoot better than a 4.75 MOA group with XM193 and the best I could do with XM855 was a 1 MOA group. Results using XM855 were inconsistent but the Sig MCX consistantly shoots a 4-5 MOA group at 50 meters with XM193.
I have come to the conclusion that the Sig MCX is not designed to shoot 5.56 as is stamped on the barrel. This should be a .223 rifle only as results with 5.56x45mm will yield unpredictable results and shooting at greater distances such as 300 meters with XM193 can result in bullet impacts up to 2.375 feet off target."

Anyone have any comments?


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Old 11-24-2016, 06:29 PM   #2
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For process of elimination, I would try some heavier bullets. 70, maybe up to 77gr.
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Old 11-25-2016, 08:50 AM   #3
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Greetings, I know I'm going to draw some ire but..

Any XM lakecity ammo failed QA, meaning it was part of a lot which was rejected. Thus I would not trust it for #@!), and I damn sure wouldn't pay premium ppr for it.

Give IMI 55/62 gr ammo a try, you can pick it up at or around .35ppr

My favorite is gecco 55gr, .33 ppr and insanely accurate out of a 1/7 twist barrel. My MCX and Ruger Takedown (1/8) love it.

Edit- one odd thing your x95 shooting that well. I passed on it because of the numerous reports of erratic accuracy, up to 5moa

Last edited by TorpedoARMED; 11-25-2016 at 08:52 AM.
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Old 11-25-2016, 10:18 AM   #4
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Yeah, that xm ammo is just good for blasting. Also, no two barrels will like the same ammo. Try some Hornady TAP 5.56 heavy weight.
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Old 11-25-2016, 10:29 AM   #5
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On the MCX/MPX weapons it is worth verifying that the barrel bolts are torqued to SIG's specs. The MCX bolts need to be torqued to 60 inch pounds.

Remington .223 has a lower pressure maximum than NATO 5.56. Hence, accuracy will be different.

The bolts on a new rifle have been known to be off spec a bit.

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Old 11-25-2016, 11:01 AM   #6
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FYI, 1" at 50 yards is 2 MOA. Not 0.5 MOA.
Oldsalt, Matt Helm and PsYkHoTiK like this.
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Old 11-27-2016, 04:21 PM   #7
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My MCX is at Sig for the same problem. At the first range trip to get it zeroed it started off OK but after maybe 8 rounds it went to **** and couldn't hold a 8" group for the next 3 mags full. I had some American Eagle 223 and some PPU 5.56 and it didn't matter...they both sucked in the MCX. The guy next to me at the range was noticing my frustration and said he ran into the same exact problem and sold his after putting 350-400 rounds of all kinds of different ammo through it, none of which shot even close to respectable. So it appears that occasionally you might get a MCX that can't hit the broad side of a barn consistently. Hopefully Sig puts a new barrel on it or just does something to get it shooting like it should. The good news is that there are plenty of reviews of people having very good accuracy. Luckily for me, Sig is 40 minutes from me...but it's been there for three weeks and still no word. I was planning on calling them tomorrow for an update.

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Old 11-27-2016, 05:23 PM   #8
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Had a fairly disappointing 1st trip to thensure range with mine as well.
Bought a case of IMI 55gr 5.56 and could not get anything better than about a 6-8 in group.
Had a bit better luck with .223 75gr match ammo. Gonna grab an ammo buffet and head back next week to see if I can find anything that works. If not I guess it will going back to SIG.
What was the MFG date on yours? Mine was Oct. 27th 16.
Wonder if there has been some recent issues in production.
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Old 11-29-2016, 04:12 AM   #9
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Real quick, MCX has a 1:7 twist-rate and likes the heavier grain bullet. See the following thread regarding differing results for the MCX. I personally (on page 6 of this thread) posted my most recent results comparing 9 different brands of .223 and 5.56. Good luck!

SIG MCX 16" 13 Ammo Range Report
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Old 11-29-2016, 05:17 AM   #10
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Originally Posted by Duckman View Post
FYI, 1" at 50 yards is 2 MOA. Not 0.5 MOA.
Yup, the math is off.

And XM193 is not "sub minute of angle" ammunition in any rifle.

I do believe that there is something wrong with your rifle and I hope that SIG straightens it out for you.

Last edited by Oldsalt; 11-29-2016 at 05:32 AM.
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Old 11-30-2016, 11:22 AM   #11
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I am also having a "fun" time finding ammo it likes. Gonna run a few tests this weekend and will add to the other big thread on this issue.
The 1st shop I started at does have a 25 yard range and I played in there for a bit.
I eliminated:
55g IMI 5.56
55g American Eagle 223 (3240 AE 223M)
55g American Eagle 5.56 (3020 XM193AF30)
55g Federal 223 (Walmart)
All shot like garbage.
It liked:
55g PMC Bronze 223 FMJ-BT (223A)
62g Winchester 62g FMJ (NOT GREEN TIP)

Gonna try some GT ammo and some heavier stuff and also may try pulling the muzzle break off to see if it is a harmonic issue.
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Old 11-30-2016, 12:30 PM   #12
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Get some of the IMI Razor 77 grain, or 69 grain 5.56 NATO ammunition, if you want tighter groups. The 1 turn in 7 inch rifling twist is to stabilize longer projectiles, as in the M856 Tracer rounds. Typical 55 grain projectiles are "over stabilized", to the point, if they are not perfectly "balanced" they will yaw excessively, opening up your groups.
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Old 11-30-2016, 12:43 PM   #13
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Ya, clearly heavier is better in this gun, Just looking hard to find something that shoots well that will not break the bank. Gonna run some side by side tests with a 516 as well, same barrel length, same twist, just to see what happens.
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Old 12-01-2016, 06:33 AM   #14
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Black Hills has remanufactured that is a little cheaper than their new. You might be able to find some "Ultramax" remanufactured 68 grain BTHP. Anything from 68 grain and up should be better, as most of the projectiles are "match grade".
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