This article shows you how to disassemble the APS manufactured Sig MPX gel blaster. From this point forward, we will use the term MPX to identify the gel blaster rifle and all of the variants (Titan SBB, Titan LBB).
2mm Hex Key
2x 4mm Hex Keys
Separate the Upper and Lower Receivers
The receiver is the main body block at the centre of the MPX. The receiver can be separated into two: the upper and lower receiver. The upper receiver is the attachment point for the front rail/handguard, the external barrel, the inner barrel, suppressor, etc. The lower receiver carries the gearbox, the rear shoulder stock, motor, and handgrip.
To separate the receiver, use the 4mm Hex keys on the 2 receiver pins. Located at the front of the receiver, right under and behind the rail/handguard. Use a hex key on either side and unscrew. It was a snug fit on the front one, requiring a bit more of force to tap it out.
Once the receiver pins have been completely tapped out, you can slide the upper receiver forward, while pulling the lower receiver backwards.
Removing the Handgrip
The MPX uses a v2 gearbox, so the handgrip is attached to the bottom of the gearbox and houses the motor. The base of the handgrip has a plate with two small screws. The big flat screw in the middle is to adjust the motor tension to the gearbox. Using a Phillips screwdriver, unscrew the two small screws to remove the plate.
After removing the handgrip base plate, you’ll see the motor and attached wires. Detach the wires and remove the motor.
Next step is to remove the handgrip. There are two screws inside the motor housing. Unscrew the two screws with a Phillips screwdriver. Be careful that the screws don’t fall into the gearbox. Once you’ve unscrewed the handgrip, you can remove it easily.
After removing the handgrip, you’ll see the bottom of the v2 gearbox. What do you know… there are actually 4 screw holes!
Separate the Gearbox From the Lower Receiver
To separate the gearbox from the lower receiver, you’ll have to tap out one receiver pin. I used the 2mm hex key and a rubber mallet. The receiver pin is just forward of the selector switch. The photo below shows the receiver pin half tapped out.
Next, remove the magazine release. With the right side of the receiver on top, use a 2mm hex key to unscrew the magazine release button. Be careful you don’t lose the spring under it.
For ease of removal put the selector switch into safe ‘No Pew’. Then remove the selector switches with the 2mm hex key. Unlike your typical M4 this has to happen as they are slightly recessed into the APS Silver Edge box for the ambidextrous gearing.
Be super careful not to lose the small ball bearings which give that tactile ‘click’ as you select fire modes. They are held in with a spring so just hold down the switch and unscrew it on a level bench etc.
By this stage, the box can move around a bit in the receiver. To remove the bolt catch mechanism. Pull the gearbox out of the receiver slightly until you have revealed the latch. Flip the receiver over to the left side. The latch is held in place with a split pin, I used the 1.5mm Hex (or a similar diameter punch) to tap it out towards the front of the MPX.
It took a bit of wiggling but the latch pulls out of the receiver, freeing up the gearbox to be removed. The selector gears are freely moving around and there is a good chance they will drop out as you remove the box from the receiver.
This is a work in progress, I’m saving it all as I go!