I have finally had the time to put together a more detailed response and description on how I solved the flash hider removal problem on my Sig Sauer MCX Rattler in 5.56. You can remove pieces from anything. Enough brute force or enough heat will do the trick. The problem is , then what? The complete answers are more complicated than need be, but some details are required because of the many different Sig Sauer platforms, the similarity in naming, and the confusions on the internet.
You must first understand the exact platform with which we are dealing. The answers in this post only apply to the Sig Sauer MCX Rattler platform, NOT to any of the other Sig weapons! Not even the other MCX’s.
Only the Rattler. To ensure everyone understands this I must list some of the Sig platforms.
Sig Sauer MCX Rattler
5.5” Barrel
5.56 or 300 BO Calibers
Sig Sauer MCX (Pistol, CQB, Tactical Patrol, Patrol) (Not The Rattler!)
9” Barrel 300 BO Pistol or 9” Barrel 5.56 Pistol, or
11.5” Barrel 300 BO CQB or 11.5” Barrel 5.56 CQB, or
14.5” Barrel 300 BO Tactical Patrol or 14.5” Barrel 5.56 Tactical Patrol, or
16” Barrel 300 BO Patrol or 16” Barrel 5.56 Patrol
Sig Sauer MCX Virtus (Virtus Pistol, Spear, Virtus Patrol) (Not The Rattler!)
9” Barrel 300 BO Virtus Pistol or 11.5” Barrel 5.56 Virtus Pistol, or
13” Barrel 277 Fury Spear, or
16” Barrel 5.56 Virtus Patrol
Sig Sauer MPX (Copperhead – K – PCC) (Not The Rattler!)
3.5”-4.5” Barrel 9mm Copperhead, or
4.5” Barrel 9mm K, or
16” Barrel 9mm PCC
The below information and solution applies ONLY to the Rattler! Other MCX’s and the MPX’s are different. Different flash hider installation. Different barrel threading. Different thread direction. When you see something on the internet and they say that for a Sig MCX you do X, Y, and Z that does
NOT guarantee it applies to the Rattler. You must be sure that any advice is specifically for a Rattler. Now let’s focus on the 5.56 Rattler and how I resolved my issues.
Following the MCX manual for “Two Position Gas Valve” settings, is very hard to do as the advice seems contradictory. It does not provide enough specifics to be very clear.
The Sig Sauer Service Manual has a somewhat more useful explanation of the settings. This page from the Service Manual was provided to me by Sig:
“The MCX platform has two different gas settings, + and -. The plus setting will allow more gas to cycle the bolt carrier. When adding a silencer to a firearm, the silencer will add ‘back pressure’ and cycle the bolt without the need for the full amount of gas. For this reason, the firearm has the option to run on the minus setting. Less gas will put less strain on the internal components and the user will experience less gas blow back. Below is the guideline for when to use each setting:”
The gas system in the 5.56 Rattler is designed to function in the “+“ position with the OEM flash hider under “normal” conditions. The 5.56 Rattler is designed to function in the “-“ position when using a suppressor.
In 2020 I corresponded with Sig directly on the flash hider removal subject for the Rattler in 5.56. Here is their answer to each of my questions:
1) Is the OEM flash hider also welded or braised onto the barrel? (A)
It is pinned and welded.
2) Is the barrel threaded? If so, what thread? (A)
Yes, a standard ½ X 28
3) Would installing a different flash hider affect the gas operation? (A)
Most likely but not in a dramatic way.
4) I do not want to screw up the firearm & will not change the flash hider if there are issues. (A)
We do not recommend removal of the flash hider currently installed by the factory. It’s a $600 mistake to correct if things go wrong.
My goal was not to mount a suppressor, but rather to obtain a reduction in felt concussion using the barrel in 5.56. I have read several articles about issues when suppressing 5.56 in this short a barrel length. If you want to mount a suppressor, you are much better off purchasing the 300 Blackout barrel change/over setup from Sig. I have done this and it works fine. If you are wanting a different flash hider for the 5.56, read below to see how I solved the problem.
To reduce the horrendous muzzle blast in the 5.56 Rattler, I ended up machining on the lathe a knock-off of the Noveske Flash Hider device which slide fits (Noveske only makes screw on devices) over the OEM flash hider and is held in place with screws drilled into that OEM flash hider. It made a night and day difference in shooting comfort while only adding about 2 ¾” in length. To me well worth the tradeoff.
Adding my Noveske type flash hider works similar to a suppressor, by slightly delaying much of the gas from exiting the muzzle. This lengthening of the time for gas exit causes higher pressure. The higher pressure is enough to cause failure to eject and feed malfunctions.
The Rattler’s changeable caliber barrel setup (Either in 5.56 or 300 BO) is purchased with the switchable gas port system permanently attached to the barrel.
Since both Rattler caliber setups (5.56 & 300 BO) have their own gas port attached to each barrel, I was not worried about gas port size modifications if necessary, having an effect when the opposite barrel was installed.
Testing with my Noveske type hider installed, I at first used the 5.56 barrel normal “+” position (Larger gas port valve hole). This caused full malfunction, with the spent case either not ejecting or a fresh round not chambering. Switching the setting to the “-“ position (Smaller gas port valve hole) solved those problems. Occasionally the bolt would still not lock open at an empty magazine.
This only issue occurs infrequently enough that I have not tampered with the gas port valve hole size. Frankly I am not sure if the gas port hole on the “-“ side needs to be slightly larger or smaller to correct the occurrences.
If one wishes to install another aftermarket type flash hider, the weapon would have to go to someone willing to do the work required to unsolder or unweld the pin to unscrew the barrel. I just did not see the benefit of going that direction.
Here are two images of my Rattler in 5.56 with my home machined Noveske type flash hider installed.
