I’ve had A LOT of requests to do an MP7 Fusion Engine conversion, but it’s such a small airsoft gun, I knew any implementation would be pretty extreme to have the Fusion Engine fit. There is only about 3.5″ of space in the MP7 where the gearbox resides. A few months ago I attempted an MP7 implementation using a cheaper quality Umarex HK MP7 and spare Fusion Engine parts, and the conversion did not go well, so I set it aside, not sure if I’d ever want to attempt it again. But after getting inspiration from SilentCustom and his Fusion Engine conversion of the TM MP7 (the first one!), and some discussion with Emil Damgaard (Denmark), I decided to give it another try with a TM MP7. Ross Abrina sent me his TM MP7 to convert and I set about cutting up the Fusion Engine.
(Note, this conversion will work with the Well R4 MP7 also, as it’s an exact copy of the TM MP7)
The TM MP7 is a pretty difficult conversion, simply due to the limited space for all the necessary Fusion Engine parts. To have it all fit, the Fusion Engine upper cylinder essentially had to be cut in half. The back of the upper cylinder had to then be sealed. With the solenoid manifold section cut away, the solenoids had to be remote from the cylinder and new pressure input taps had to be added. A new gunside macroline connector is also added to connect the Engine to the air rig.
I tried multiple configurations of solenoid placement and poppet and nozzle valve connection placement. I ended up replacing the large poppet and nozzle valve banjo connectors with smaller 3mm connectors and placed the solenoids on top of the Fusion Engine cylinder. I added a mounting block to the bottom of the engine held in place with a zip tie. There weren’t any convenient places to drill holes into the front cylinder because they would interfere with the large nozzle o-ring, so a shallow band was lathed into the front cylinder and a zip tie was used to fix it to the mounting block. The recessed band was needed so the zip tie doesn’t bind against the sliding stock arms. The mount block was 3D printed, made from solid ABS (I could have machined it from aluminum, but I wanted to try out my new 3D printer…more on that another time). The mount block is then screwed to the bottom of the MP7 receiver and it’s sufficient to hold the Fusion Engine cylinder in place.
The solenoids, with the air line elbows attached, are too wide for the MP7 body, so they have to sit at odd angles to allow the body halves to fit, as well as make room for the sliding stock arms. The placement and length of the solenoid air lines is critical in holding the solenoids in the correct location and orientation.
The stock MP7 trigger switch is used, wired to the small circuit board. A new microswitch had to be added to support the fire select functionality. There are several potential locations for the switch but I ended up putting it on top of the main trigger switch assembly. A custom length wire harness is used to allow the FCU and battery to be in the front of the MP7. A very small 180 mah 7.4 lipo battery is needed to have it all fit in the small battery compartment.
The MP7 hopup is smaller than a standard hopup, so the Fusion Engine nozzle had to be lathed down about 0.5mm to decrease it’s outer diameter so it would fit into the hopup. The length of the nozzle turned out be the the same as the standard M249 nozzle.
A clearance cut is also needed on the bottom of the front cylinder to allow the MP7 magazines to fit properly. Also, some extra plastic rails from the inside of the body halves needed to be sanded off to make room for the Fusion Engine cylinder.
With the solenoids on top of the Fusion Engine, there isn’t enough room for the ejection port dust cover, so it is removed and the hopup is exposed (maybe a good thing for easy access to the adjustment dial). The charging bolt handle on the back is fixed in place since it is no longer used to pull back the dust cover.
The MP7 conversion is rather difficult, and maintaining the gun is a little daunting. It requires patience if you dare to open up the gun as reassembly requires all the parts to fit back into the gun very precisely and with great care. But for the ultimate in maneuverability and light load out, the PolarStar Fusion Engine MP7 is currently the smallest P* gun out there!