As I mentioned in my previous thread about the Sig Sauer MPX’s trigger, I’ve been loving my Sig Sauer MPX. But as time goes on, a few nagging little issues have reared their heads. First, it was the aforementioned trigger issue, and the “confusion” over whether an aftermarket AR-15 trigger group will void the warranty. Now it’s the charging handle, which while based on the AR-15 design, is a part unique to the MPX. The first time I actuated the aluminum charging handle, I remember thinking it felt a tad flimsy. What I was actually feeling, however, was about a quarter-inch of play in the shaft of the handle when it’s extended. Notice how the shaft of the handle slopes slightly downward, until it rests right at the point where the upper and lower meet on the top side of the firearm:

Side view of the Sig MPX’s charging handle (courtesy of Dieseljayy of SigForum).

What’s Causing the MPX Charging Handle Issue

According to DieselJayy of SigForum, the issue stems from the fact that while the MPX might have an AR-15-inspired charging handle, there’s at least one major difference between how the charging handle on both weapons interface with the bolt carrier group (or “BCG”). On an AR-15, the charging handle grabs on to a bolt key to move the bolt carrier group rearward when charging — which sits above the BCG (and recoil system) on a standard AR-15. On the MPX, the recoil system is above the BCG, rather than in-line with it as on a standard AR-15, and therefore has no bolt key, so the charging handle on the MPX has to pull on a small lip on the BCG that’s in-line with the recoil springs:

Sig MPX bolt carrier group lip where it interfaces with the charging handle (courtesy of Dieseljayy of SigForum).

As a result, when the MPX is fired and the bolt cycled, the charging handle needs to remain out of the way of the metal lip. The MPX’s charging handle has lower sidewalls than an AR-15, and so when it’s pulled back, those lower walls cause the handle to sag downward, as shown in the first photo above. When the charging handle is released from its extended position (such as when hitting the bolt release button after loading a new magazine), the speed and angle of the charging handle returning to its closed position cause it to “bounce” off the rear section of the firearm. This causes two issues. First is a not-so-serious cosmetic wear mark on the rear portion of the lower (as seen on my MPX):

Cosmetic wear on the rear portion of my MPX’s lower.

But the second issue is more serious, as the charging is chipping away at the rear portion of the MPX’s upper, actually digging into the upper and removing metal. Here’s the damage on my MPX that has relative few rounds through it so far:

Damage caused by my MPX’s charging handle to the upper.

The chips in the upper are even more pronounced on Dieseljayy’s MPX, which has cycled 10K+ rounds as of this writing:

Chipping of the upper on Dieseljayy’s MPX (courtesy of Diesljayy of SigForum).

Overhead view of Dieseljayy’s MPX upper (courtesy of Dieseljayy).

Take a look at the underside of my charging handle to see where the rounded corner portion is impacting the upper and chipping the metal (and also causing wear on that portion of the handle):

Underside of a Sig MPX charging handle, showing where it’s impacting the upper.

How to “Fix” the MPX Charging Handle Issue

With the cause of the problem identified, the obvious fix would seem to be a redesigned charging handle from Sig Sauer, or perhaps even some sort of add-on piece that helps support the MPX’s charging handle and keep it elevated when fully extended. But until that happens, MPX owners will have to resort to Velcro and paperclips.

You read that right.

Velcro.

And paperclips.

On a Sig!

I’m certain Friedrich Peyer im Hof, Heinrich Moser and Conrad Neher are turning over in their graves…

Yes, a number of MPX owners are putting a small strip of adhesive “fuzzy-side” velcro on the rear portion of their lower where the cosmetic wear occurs. This also slightly supports the charging handle in its extended position, and helps prevent the chipping and wear. However, this  approach has also been shown to cause misfeeds, so SigForum member Dieseljayy developed the “MPX paperclip fix.”

installing a paperclip folded liks this in an MPX can help lift the charging handle to avoid wear (courtesy of Dieseljayy).

In his words:

 The only thing we need to do is add something like a spring to push the charging handle up to it stays parallel to the top rail. This would prevent it from hitting the receiver when you release the charging handle. My spring of choice. A paperclip. I was trying to find a way to attach something to the piece of metal that holds the guide rods in place but since I didn’t want anything that would mod the gun I used the recoil buffer to be the perfect candidate for a mounting surface.

Now all you have to do is bend a paperclip in a circle around the screw behind your buffer and tighten it down. Then bend a 45 degree angle upwards off the buffer pad. This will give the spring enough clearance that it won’t hit the BCG when it cycles. Take the top part and coil it a few times so it only has a smooth surface that will be hitting the underside channel of the charging handle. Line it up so when you attach the upper it goes in front of the plate that holds the guide rods. That is all you have to do.
Now the paperclip will be applying upward force to the charging handle after it’s been released preventing it from scratching up your lower receiver and your upper.

Now some to answer some concerns with this design.

1. The BCG does not impact the paperclip. It stops 3mm short of hitting my setup from the buffer.
2. I’ve already ran 500 round through this design and the paperclip still works like new since there is 0 stress on the paperclip.
3. The OAL of the buffer on the back of the receiver did not move closer to the BCG with the paperclip behind it when tightened down.
4. I used a thin piece of packing tap after sanding the paper clip that will be pressed by the buffer into the receiver so it doesn’t scratch the receiver behind the buffer.
5. The underside of the charging handle is not scratched by the paperclip. The paperclip is to soft of a material.
6. This is my temp fix until Sig can come out with a real part. (Basically they just need to mod the part that holds the guide rod with a piece of metal pushing upward and that will fix this.) It is not complicated…

Bend the paperclip around the buffer screw and tighten it down (courtesy of Dieseljayy).

The paperclip applies upward force to the charging handle, which prevents wear to the upper and lower (courtesy of Dieseljayy).

The paperclip fix can be seen when the charging handle is pulled back (courtesy of Dieseljayy).

As far as the legalities and liabilities of this approach, anyone who tries it is obviously 100% on their own. Dieseljayy made it clear in his post that any modifications to your MPX are done at your own risk. Any damage caused to your MPX as a result of attempting this procedure will most likely not be covered by Sig Sauer’s warranty. He also estimates that the paperclip might last as long as 3K rounds or so before it would lose enough spring tension that it needs to be replaced.

MPX Owner Reactions

Sig Sauer President and CEO Ron Cohen is quoted as saying at SIG’s Media Day and Factory tour as saying “We’re gonna make a bad gun today…but the reaction of SIG will make you proud of us” — implying that while SIG (like any company) is bound to make mistakes along the way, the way they respond to those mistakes will keep owners happy.

So are MPX owners feeling proud? For the most part, no. At least one owner that I know of returned his MPX to Sig for this issue, and was told by a Sig rep that they had “repaired the scaring and sent it back.” However, when he received his MPX back, the paperwork said “Inspected the pistol, wear marks from the charging handle are normal and inherent to the design,” and the gun was returned in the same condition as sent. Another, while referencing Cohen’s quote, commented that he’d clearly misinterpreted Cohen’s intent, because he “was foolish enough to spend $1,300 on an MPX.”

I called Sig Sauer Customer Service myself to inquire about the issue. They were polite and professional as always. The rep I spoke with put me on a brief hold, discussed the issue with one of the gunsmith’s in the office, and then passed on the gunsmith’s words that it’s “perfectly normal,” “happens on all of of them,” and “does not impact the functioning of the firearm.” He also told me they had no current fix planned, but that the gunsmiths were aware of the issue and “might” issue a fix in the future.

For me, the jury’s still out on how SIG is handling the issue. It’s clear they’re aware of it, but there’s been no public acknowledgement (that I know of) that the issue even exists. As a result, I see a big opportunity for a third-party manufacturer to possibly develop and sell an aftermarket MPX charging handle that doesn’t sag when extended, or perhaps a variation on the paperclip fix involving a strip of spring steel mounted on the buffer screw. I’d be the first in line to purchase either of those options.

Until then, it appears that MPX owners looking to avoid wear and chipping on their firearm will have to resort to Velcro and paperclips on their gun… and keep a bottle of Birchwood Casey Aluminum Black on hand. 🙂

Comments, questions, or feedback? I’d love to hear from you below!

Further Reading:

• Original paperclip fix post on AR15.com by Dieseljayy/Jaysondiesel
• Sig Sauer MPX Thread on SigForum.com