Umarex MP40 Problems: 4 Problems and Solutions!

Imagine this, your favorite MP40 fails to function properly in a shooting range. You must feel frustrated and we totally understand you. So, don’t worry we got you covered.

Wondering how to fix Umarex MP40 Problems? 

Umarex MP40 overtime faces many problems. It can be a CO2 air leak, which causes FPS to drop while shooting. However, it can be a magazine problem for which feeding bb can be hard. Lastly, there can be misfires which can cause severe damage to people. The problems are various, so are the solutions.

All the problems can be confusing at first. For this reason, we have provided everything in detail so that you find a suitable solution.

Let’s begin, shall we!

Things to Know Before Jumping in

Umarex MP40 is a popular airsoft submachine gun. With a velocity of 450 fps, the gun can hold 52 CO2 metal BBs per round. The submachine gun weighs about 7.7 pounds.

This airsoft gun has the main components made out of metal. So, maintaining this gun is critical. Otherwise, many problems may arise. 

However, even with proper care, Umarex manufacturers’ airsoft guns face problems. For instance, Umarex Origin problems are notable. Moreover, the Umarex MP40 has some problems too.

Troubleshooting Umarex MP40 Problems

Even though the Umarex MP40 is a renowned gun, there are a few problems you might face. So, we have covered everything about the problems and provided solutions.

Before we dive deep into the solutions you need to be cautious. Umarex MP40 disassembly will lead to a warranty void. So, after going through the article if you want to DIY just bear this in mind.

Now, let’s get started!

Problem 1 of 4: CO2 Air Leaks

As mentioned before, Umarex MP40 is operable with CO2 cartridges.CO2 airsoft guns one of the common problems is this.

In order to troubleshoot, first, recognize where the problem is occurring. This can either be from valve leakage or cartridge seal. If CO2 air leaks, then the FPS of your MP40 will drop drastically.


You can use Teflon tape as a fast repair for seal-related problems. Apply tape to the top and sides of your MP40 gas canisters. This ensures that the canister fits perfectly and prevents the distorted seal from leaking CO2. We recommend using Dixon Valve for this.

The gas in your MP40 cartridge is kept from leaking out by a pin with a seal. When you take the magazine out of the rifle, the pin is visible.

Apply a generous amount of airgun lubricating oil to the seal. Also, repeat the procedure every time you load a brand new cartridge. Using Crosman 241 pellgunoil is ideal as lubricating oil to protect the seal.

If the CO2 from your MP40 cartridge is leaking fast, it’s probably time to replace it. It is best to purchase a new cartridge seal to avoid more complications. Learn more about whether or not all CO2 cartridges are the same.

Problem 2 of 4: Magazine Problem

Umarex MP40 magazine problems are worrisome. For Umarex MP40 magazine problems, you may not be able to use MP40 to its full potential. 

Due to faulty manufacture, you may be unable to feed the full magazine to your MP40. Other issues include the MP40’s air nozzle being pushed back, preventing bullets from being fired.


You need to check hop-up settings for BB feeding. Tilt the hop-up away from the mechbox’s front. This is done by moving the material on the back of the hop-up. So it sits more in front of the Gearbox shell. 

It’s important to keep in mind that this should be done in modest steps. If you tilt too much, you’ll lose a lot of frames per second. Hard rubber can be used if it can be sanded and cut to form.

Problem 3 of 4: Misfires

Misfires in a shooting range can weigh heavily. It not only wastes your precious BB, but it also causes friendly fire. Sometimes because of the problem, serious injury occurs. Inappropriate Umarex MP40 mods can cause this problem to occur.

Misfires of MP40 can be caused by improper magazine insertion. The solutions for the problem are as follows,


For improper magazine insertion, the fix is easy. Simply remove the magazine, top up with gas, and re-insert it. This time, make sure it’s correctly inserted and attached to the MP40.

Problem 4 of 4: Noise

An average airsoft gun produces a sound of 80 to 96 dB. Whereas, the real gun produces 140dB. If your MP40 is making a loud screeching sound or grinding sound then it’s a problem.

By grinding sound or screeching sound it may mean one of the important components is busted. The components can be gear, ball bearing, piston, pinion gear, etc.

However, solutions to the problems are straightforward.


For pinion gear shimmed too far away from the bevel can cause insufficient results. So, shim the top of the bevel gear to force it to engage the pinion with shims.

After troubleshooting you see stripped gear is busted, then you need to get a new one.

For exploded ball bearings, you need to replace them and get a new one too. AOLS is one of the best in the market.

Lastly, if you want to turn down the noise, then use a silencer. Acetech is the favorite choice of airsoft lovers.

The main and most common problems with Umarex MP40 are listed above. We’ve discussed the difficulties as well as the solutions. Hopefully, the solutions will all be useful to you. If problems are not fixable, consulting a professional is wise.

However, be careful while fixing the problems. CO2 gas from the gun’s cartridge can give you asphyxia

Let’s now go to the next step.


Using airsoft guns, especially MP40 is fun and entertaining in any airsoft game. However, in order for your MP40 to last longer, you have to take proper steps to maintain them. Fortunately, maintaining your gun won’t be that hard. Here are some tips,

Keep Your Weapon Clean

Maintain the cleanliness of your weapon. Soot, filth, and debris should be removed from your weapon to ensure that it performs best. This stage should also involve inspecting the barrel for any remaining bbs.

Take Care of the Magazines

Keep your magazines in good shape. When not in use, make sure they’re not wound or loaded. This prevents undue pressure on the internal systems.

Store it Properly

Maintain appropriate storage for your firearms and equipment. Keep it out of direct sunlight and in a cool, dry location. To avoid any form of injury, do not cram them into a small place.

Here, we’ve discussed 3 maintenance factors. By following these factors you can keep your Umarex MP40 in pristine condition.


What is the range of the Umarex MP40?

The Umarex MP40 has a range of 10 yards for maximum accuracy. But, you can increase the accuracy by adding sights and scopes.

What is the velocity of Umarex MP40?

At the ideal temperature, the gun has a max velocity of 465fps. However, it changes considering several situations like weather, gun wear, and tear, etc.

How Many Shots Can be Fired per CO2 cartridge of Umarex MP40?

120 to 160 bbs can be shot per CO2 cartridge of Umarex MP40. After that, you’ve to change the CO2 cartridge. 


That’s all from us about Umarex MP40 Problems. We hope that the article cleared up every confusion and you found a proper solution.

Here’s a catch! Airsoft guns are delicate and require a lot of attention while fixing. If you are still facing trouble then consulting a professional is a wise decision.

See you soon!

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