Modding the LPEG P90

Replace the Tri-Rail upper receiver

FN P90 Replica

What you'll need: recommends the use of proper eye protection and respirator/dust mask equipment whenever working on props. This site will not be held liable for injuries resulting from following these tutorials.

Eye protection:

Lenses should be made from polycarbonate to protect from flying debris.


Completely cover mouth and nose, and fit the form of your face. A mask with interchangeable P100 particulate filters is recommended for this project.


This tutorial will take you through preparing an LPEG P90 airsoft gun for conversion into a standard model P90. This involves cutting off the current Tri-Rail upper receiver, and replacing it with the P90 kit. You can obtain the airsoft P90 from many online sources including airsoft shops and auction websites. The average price for these is $30-$40 shipped in the USA.

For availability of the P90 upper receiver kit, please e-mail

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Starting out

As with most projects, start by organizing a clear work space. You should ideally have enough space to lay out the airsoft rifle, and to keep your tools within easy reach. This project will involve a moderate level of cutting/sanding, so you should expect plastic shavings and or dust.

P90 Cocking Handles
Remove and discard

The first step is to remove the cocking handles from each side of the airsoft gun. These are held on with phillips head screws. Remove both cocking handles and discard (we won't be reusing them).

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Carry on

Pull forward and off
P90 Magazine Release
Remove the mag catch

The next part that needs to be removed is the magazine release on the top of the gun body. This is a "u" shaped piece that is located at the rear of where the magazine sits. To remove the part, insert a flat-head screwdriver under the piece from the side and gently lift. Do this to each side, and the piece will move forward. WARNING: this piece is spring loaded. Be careful not to lose the small spring located behind the piece. Once removed, place the part into the bag or box that you will be storing parts in. We will be reusing this part, so save it and the spring.

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Breaking it all down

Airsoft P90 shell split
Gently pry apart

Once the mag catch is removed we can focus on taking the gun apart. The P90 is made in two halves that are secured together by screws. The screws are accessible from the right hand side of the gun. There are approximately 16 screws that you will need to remove. It is easy to miss the one holding the right-side rail on, but you will need to remove it as well (the rail will then come off as well).

Open up the LPEG P90
Go all around

Once all of the screws have been removed, the next step is to begin splitting the gun body in half along the seam line. Ensure that the gun is laid out on its left hand side. For this, use your flat-head screwdriver to gently pry the gun apart. Use soft pressure, and work your way around the entire gun before attempting to lift off the right half. If you can't separate the gun, or if there is resistance in one area, then go back and check to make sure that you removed all of the screws.

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Split the difference

Airsoft gun opened up
Naked gun ...

You will now be able to lift off the right side shell of the gun. Lift it off carefully so that no small parts are lost. Once you have lifted the right half, inspect the inside to insure there are no parts attached. All internal parts are normally located on the left half of the gun body, but it's safe to check so that you don't lose anything by mistake.

Once inspected, place the right half of the gun shell somewhere safe.

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Gut the internals

P90 fire selector
Safety pin + spring
Pull out the safety switch
Grasp the safety pin

The last step in disassembling the gun is to remove all of the internal components. Start by removing these components:

P90 Trigger Removed
Trigger and spring

Now it's time to remove the trigger and safety assembly. Later, we will be reinstalling it in the same exact way--so observe how it is installed! Start the removal process by carefully taking out the pin below the safety (on/off) switch. This pin has a spring inside of it, so grasp it securely with a finger at the top and bottom. Now you can remove the trigger. Again, be careful not to lose the spring. The safety switch will now come out as well.

Take out the LPEG gearbox
Mechbox removal

Finally, remove the electronic switch that used to be attached to the trigger. Once removed, you will now be able to lift the gearbox out of the gun. We will not need to reinstall it, so either discard it or save it for another project.

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Shell of a P90

Unassembled Airsoft P90
Empty gun

Congratulations, you've successfully taken apart the P90 airsoft gun! On the next page we will do the final preparation work needed before installing the new upper receiver.

>> Modifying the LPEG P90 - Page 2 >>

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