Introduction

My modified Nerf Longshot (nicknamed: Leviathan) is a significant powerhouse compared to most stock foam dart blasters. Although I have yet to measure the muzzle velocity of the Leviathan, I can visually notice double the muzzle velocity compared to stock nerf blasters, at least 140 feet per second (FPS) versus 70 FPS. The reason for a high FPS comes down to a powerful spring pushing a plunger forward in an airtight tube to force air into the firing chamber where the dart lies, propelling the dart through an airtight inner barrel for a high muzzle velocity. However, the plunger needs an O-ring as an air seal, and worn-out O-rings will slip off the plunger, disabling the blaster. I will show you how to replace the O-ring in this guide.

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    • Caution: Do not disassemble when the blaster is primed (spring potential energy stored). Disassembling while primed will extend the plunger arm, locking the plunger tube in, and releasing the spring disassembled can scatter and damage internal parts.

    • You can tell the blaster is not primed when the spring pushes the front pump handle or side handle.

    • If the blaster is primed, you can release the spring tension by pulling the trigger.

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    • Remove the outer barrel attachment and optic.

    • If your optic is attached via a Picatinny rail, also remove the rail by reversing the installation steps.

    • Leave the inner barrel alone as it has no involvement in this fix.

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    • Remove the screws from the pump-action handle using a Phillips #00 screwdriver.

    • Skip this part if the handle is not installed.

    • Remove the six screws from the stock using a Phillips #00 screwdriver.

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    • Remove all screws holding the blaster shell together using a Phillips #00 screwdriver.

    • Check the pistol grip and stock mount for more screws.

    • Two screws are longer than the rest.

    • Two screws are shorter than the rest.

    • Remember the positions of these screws when reassembling.

    • Consider using a magnet to pick up all loose screws.

    • Lift the top half and set it aside to reveal the internals.

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    • Remove the screws from the arch holding the plunger arm and plunger tube in place.

    • Remove the plunger tube.

    • A spudger can provide leverage to help remove the arch.

    • My part broke due to the high stress of the spring, but there are no consequences if it happens to you.

    • Some models do not have this part. If so, skip this step.

    • The orange nerf rail tooth and corresponding spring may fly out during the fix. If so, neatly set them aside, but make sure to reinstall during reassembly.

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    • Remove the screws connecting the plunger tube end cap to the plunger tube using a Phillips #00 screwdriver.

    • Pull out the plunger to reveal the worn-out O-ring on the plunger head.

    • When reassembling, a strong spring will increase the risk of stripping the screws and difficulty in reassembly. Use a screwdriver slightly bigger than the slot and push hard into the end cap for the best results.

    • You can tell if your O-ring is worn-out when it swells past its advertised dimensions, allowing it to sag or slip.

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    • Use a spudger to remove the worn-out O-ring and then install the new one.

    • Consider applying a thin layer of lubricant around the new O-ring for smooth operation.

    • Avoid combining silicone O-rings with silicone lubricant since the lubricant will cause the O-ring to swell and increase the likelihood of slippage. In fact, this error inspired me to create this guide.

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    • Reassemble the blaster by reversing steps 2-6, starting at 6 and ending at 2.

    • If the blaster shell halves will not connect, double-check if the plunger tube (red) and the bolt sled (orange) are firmly in place.

Conclusion

With all maintenance completed, the Leviathan is back on the hunt. Good hunting, Nerf snipers.

Jamie Ho

Member since: 05/04/22

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