5 Main Mossberg 940 JM PRO Problems And How To Fix Them

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Recently, I got my hands on the Mossberg 940 JM PRO and took it out for a test drive. Let me tell you, it’s a solid shotgun, no doubt. But, like any piece of machinery, it had some issues that came up while I was using it. 

Now, what problems did I come across, you ask? I found that the shotgun sometimes had jamming issues, feeding problems, a quirky safety button, and occasional ejection issues. No need to fret, though. I’ve dug deep to find the solutions for each of these issues.

This article aims to guide you through these common iMossberg 940 JM PRO Problems and offer straightforward solutions to make your experience with the Mossberg 940 JM PRO as smooth as possible. 

Overview of the Problems & their Solutions

Jamming IssuesClean chamber, switch ammo, replace shell elevator springs
Feeding ProblemReplace shell latch, upgrade follower in magazine tube
Problem with Safety ButtonClean or replace with aftermarket safety button
Cycling IssueClean gas system, check action bars, replace action spring
Issue with the EjectionClean and lubricate, replace ejector and its spring

Top 5 Mossberg 940 JM PRO Problems Problems & Solutions

1. Jamming Issues 

Alright, let’s kick things off with the jamming issue. When I took this shotgun out to the field, it was all fun and games until a jam. 

The bolt wouldn’t return to its starting position, making it impossible to fire another round. It didn’t happen every single time, but enough to notice. 

It’s frustrating, especially when you’re out there, focused, and suddenly the gun jams on you. That can throw off your entire session.


So, how did I tackle this? First, I thoroughly cleaned the chamber and the magazine tube. Sometimes, dirt or debris can be the culprit. Didn’t completely solve it, but it helped. Then, I turned to my next solution: switching ammo. 

Different ammo has different coatings, and some worked better than others. Lastly, I checked the tension of the shell elevator springs and even replaced them. Guess what? The jamming issue pretty much vanished. 

Maintaining your shotgun, changing the springs when needed, and being mindful of the ammo you use is crucial. Trust me, it makes a difference.

2. Feeding Problem

Ah, the feeding problem. Been there, done that. So, there I was, aiming at a target, pulled the trigger, and… nothing. 

The shell wouldn’t feed into the chamber, and that’s a big no-no when you’re trying to focus on accuracy. I could see that the shell wasn’t properly aligned with the chamber. 

It’s like the shotgun and the shell were having a little disagreement. Annoying, right? This happened more than once, and let me tell you, it starts to get to you after a while.


Okay, let’s get to the fix. My first thought was to examine the magazine tube and the shell latch. And yep, there were signs of wear and tear. 

Replacing the shell latch made a decent difference. But what really sealed the deal was paying attention to the follower in the magazine tube. 

I got myself an upgraded, high-quality follower, which made the feeding process much smoother. It’s not rocket science, just some good old maintenance and part replacements. Doing this will save you a lot of headaches, believe me.

3. Problem with the Safety Button

Alright, now let’s talk about the safety button issue. Safety is paramount, so it’s a big deal when something’s off with the safety button. 

What I experienced was a bit of stickiness and hesitation when trying to engage or disengage the safety. At times, I had to put in a fair amount of thumb force to switch it, and that’s not what you want when time is of the essence. 

It was inconsistent, making it hard to rely on, especially in situations where quick action was necessary.


So, what’s the game plan to fix this sticky situation? First off, I removed the safety button to 

inspect it for any visible issues like rust or dirt. After a good clean, it was somewhat better but not perfect. 

So, I decided to upgrade to an aftermarket safety button, one that’s designed for smoother and quicker action. Replacing it wasn’t tough; I just followed the manual. After the swap, the safety button’s performance improved significantly.

It was easier to engage and disengage, making the firearm much more dependable. Just goes to show a small upgrade can make a world of difference.

4. Cycling Issue

So, let’s delve into another problem I came across: the cycling issue. The shotgun is supposed to automatically load a new shell after firing one, right? Well, that wasn’t always happening for me. 

I’d fire a shot, and the shotgun would hesitate instead of cycling to the next shell smoothly. It’s like it got stage fright or something. 

This problem added extra seconds to my shooting time, and every second counts when you’re trying to improve your performance.


How did I resolve this? Well, I started by cleaning the gas system thoroughly. A dirty gas system can affect the cycling speed. 

Then, I checked the action bars for any bends or irregularities. Finding none, I moved on to replacing the action spring. This spring is what helps the shotgun cycle properly, so a worn-out one can definitely cause issues. 

After the replacement, the cycling was back to its smooth self, and I could focus on my shooting instead of worrying about mechanical problems. 

Trust me, a few tweaks and replacements can turn your experience around. Don’t underestimate the power of good maintenance.

5. Issue with the Ejection

Last but definitely not least, let’s get into the ejection issue. Picture me out in the field. I take my shot, and then the used shell just lazily pops out or doesn’t eject at all. 

That’s an ejection problem for you. It got to the point where I had to manually remove the shell a couple of times. As you can guess, it breaks your flow, and it’s not something you’d expect from a shotgun like the Mossberg 940 JM PRO.


Alright, so how did I tackle this one? My first move was to clean and lubricate the ejection area and the ejector itself. 

Sometimes, it’s as simple as that. But in my case, the issue persisted. 

So I decided to replace the ejector and its spring with new ones; what do you know, it worked like a charm. Ejection was smooth, and I got my mojo back on track. 

Changing these parts isn’t complicated; refer to your manual, and you should be ready.

Final Verdict

Alright, let’s wrap things up. The Mossberg 940 JM PRO is a solid choice, don’t get me wrong. I had a blast using it, and it’s built to perform. 

However, I can’t ignore the issues I encountered—jamming, feeding problems, finicky safety button, cycling issues, and ejection trouble. While these are setbacks, none are deal-breakers, especially because each can be tackled with proactive troubleshooting. 

All machines have their ups and downs; the same goes for this shotgun. What makes it stand out, though, is how well it performs once you’ve sorted these issues out. 

My experience showed that a little maintenance and perhaps a few part replacements can go a long way. So, while the Mossberg 940 JM PRO has room for improvement, it still gets a thumbs-up from me for overall reliability and performance.


How many rounds does a Mossberg 940 JM Pro hold? 

The Mossberg 940 JM Pro holds a total of 10 rounds.

Is a 940 Pro Mossberg inertia or gas? 

The 940 Pro Mossberg is a gas-operated shotgun.

Is the Mossberg 940 reliable? 

Yes, the Mossberg 940 is known for its great reliability and affordable price.

Is Mossberg 940 better than 930? 

The Mossberg 940 is an evolution of the 930 and is considered a serious improvement, especially in advanced features.

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I'm Micheal, an avid shooter and hunting enthusiast from Texas. I'm a recreational shooter who loves to spend time at the range and enjoy learning about new firearms and gears. I love to write about guns and share my passion for shooting with others.

4 thoughts on “5 Main Mossberg 940 JM PRO Problems And How To Fix Them”

  1. How many shots did you run through the Mossberg 940 JM Pro before you started having problems? Did you clean it when you pulled it out of the box? I just bought one and plan on using it for a Helicopter Hog hunt in Texas in April and now I’m worried I will get up in the air and it be a shit show with the gun not working properly. I get 1 hour of fly time for $550 so will this gun shoot 40-60 rounds being new without me having all the problems? Let me know what you think….Thanks

    • I ran over 100 rounds through my Mossberg 940 JM Pro before noticing any issues, and yes, I did clean it straight out of the box. For your Helicopter Hog hunt, if you clean and lubricate it beforehand, and maybe test a few rounds to familiarize yourself with any quirks, you should be good to go for 40-60 rounds without a hitch. Just make sure to use quality ammo that the gun handles well. With a bit of prep, your Mossberg should perform beautifully for that thrilling hour in the air.

      • Thank you for the reply and the advice. I will definitely clean and shoot before the hunt gets here We will be using 00 Buck so it has some umph and will hopefully cycle fine.

        • Glad the advice helped! Cleaning your shotgun before the hunt and using 00 Buck sounds like a solid plan. Here’s hoping it cycles flawlessly for you.


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