PolarStar Fusion Engine Tips and Tricks, Nozzle Alignment, Safety Lever and Barrel Extensions

When adjusting nozzle alignment issues with a V2 PolarStar Fusion Engine, the most difficult alignment issue to solve is having the nozzle sit too high in the hopup. This isn’t a common problem, it often occurs when an upper receiver and lower receiver aren’t matched (from different manufacturers). One way to bring the nozzle down so it’s centered in the hopup is to add a small set screw to the back of the Fusion Engine. You can then adjust this screw as needed to bring the nozzle down. The set screw, when pushed out from the back of the Fusion Engine, presses up against the back of the lower receiver, forcing the nose of the Fusion Engine down. Without the set screw, in this case, the buffer tube screw will pull the Fusion Engine back, raising the nose of the Engine. The set screw prevents that from happening. Note that using a rear set screw as shown may cause misalignment in the pin hole above the trigger. In this cause simply leave the trigger body pin out. The Fusion Engine will be held in place by the grip screws and the rear buffer tube screw and the pin isn’t needed. You can see in the last picture the downward rake of the Fusion Engine and the missing trigger body pin. This was needed to get the nozzle centered since the upper receiver did not match the lower properly.

For the V2 PolarStar Fusion Engine, if you need to adjust the nozzle up in the hopup, you can help center the nozzle by adding a shim under the front cylinder, or, if possible, you can tighten the rear buffer tube screw (assuming the screw goes into the back of the Engine). Note that tightening the rear buffer tube screws puts pressure on the trigger body pin and the rear body pin, so have the pins installed before tightening the buffer tube screw, and loosen the buffer tube screw before removing them. For shimming, I use simple washers from the hardware store, but sometimes thinner shims are needed. Just about any material can be used a shim, even cut up business cards. If you would like different thickness washers, official P* shims are available from P* retailers.


Sometimes the placement of the V2 PolarStar Fusion Engine within a receiver causes the semi auto trigger pull to have a “bump” feel to it. This is due to the safety lever being partially engaged and when you pull the trigger; it hits the safety lever then pushes it out of the way. One way to fix this problem is to grind down the selector plate by about 1mm. This allows the selector plate to site a little further forward without engaging the safety lever. See the picture below to show the small cut in the selector plate. An alternative is to cut down the “D” part of the “P” safety lever to allow the selector plate to move forward more.

IMG_2237 P1060983_annotated

A small tip when having problems with shot accuracy and consistency. Always remove your barrel extension or flash hider when trying to solve shot consistency problems. You want to eliminate anything past the inner barrel as the potential cause for the problems. Check the extension or flash hider for any white marks, which would indicate the BBs are hitting it on the way out. The pictures below show where the BBs were hitting the end cap on this extension. There wasn’t any play with the inner barrel, so the end cap was drilled out to make the hole bigger so the BBs wouldn’t hit it.


PolarStar Fusion Engine Parts Identified

Here are some pictures that identify the various parts of the PolarStar gen3 V2 Fusion Engine. I hope this is helpful in creating a common “vocabulary” when discussing various parts of the Fusion Engine.

Happy Airsofting!

– Rudy

M2 Machine Gun PolarStar Fusion Engine Conversion

IMG_2201The The M2 Machine Gun or Browning .50 Caliber Machine Gun is very large machine gun, and it’s extremely rare to see one as an airsoft gun. Tom DiQuattro wanted to have his M2 replica converted to a PolarStar Fusion Engine gun so he sent it out to see what could be done.

The M2 replica is massive. It’s almost 6′ long, and it weighs in at 36 lbs without the box mag. It was decided that real .50 cal ammo can would be used as the box mag for the gun, and with the box mag fully loaded, the weight of the gun tops 50 lbs!

IMG_2202The replica was made with a solid aluminum barrel. It was not bored out. I attempted several tries to bore the barrel using extra long drill bits, but I just managed to mangle up the barrel (lesson learned!), so I had to ship the barrel back to Tom where he had a friend with the right equipment properly bore out the barrel. The barrel is connected to the main body of the gun by large threads. This required that the hopup be able to fit through the front of the gun, so it can be inserted with the outer barrel, since a long 650mm inner barrel would be used with the gun.

IMG_2177A G&G/CA M14 hopup was used since it had a narrow profile and could fit through the front of the gun. To hold the hopup in place, and to provide a way for a BB feed tube to attach to the hopup. a 3D printed hopup block was created. The hopup block sandwiches the hopup and locks it in place, and also supports the front of the Fusion Engine. The rear of the Fusion Engine was held in place by another 3D printed bracket, which also supported the mini circuit board and MCU box mag circuit (which links the box mag to the trigger on the FCU).

The bottom of the gun was uncovered, so another 3D printed piece was created to close up the bottom of the receiver.

IMG_2168The trigger lever on the replica was simply a metal piece held in place with a pin, pushing against a spring. To have it work with the Fusion Engine, a hard stop was added to prevent the switch from hitting the buffer tube, and a micro switch was added so it would be activated when the trigger lever was pressed.

The .50 cal ammo can was modified to hold a MAG brand box mag. A large 3D printed feed bed was used to hold the box mag mechanism in place as well as feed the BBs down into the box mag. It has a giant capacity of about 19,000 bbs!

IMG_2173The M2 Fusion Engine conversion was a bit of a challenge (especially that solid barrel), but with the extensive use of 3D printed parts (the Makerbox Replicator 2X 3D printer has been a fantastic investment), it was able to be assembled in a very user friendly and maintainable way.

When hooked up to a large air source, high BB capacity, the M2 Fusion Engine gun will provide game changing firepower to any airsoft skirmish!

Happy Airsofting!

– Rudy

Here’s are some videos of the M2 assembly and disassembly procedure:

Here’s a sustained fire test video:

(more videos coming soon)

How To Update The PolarStar Fusion Engine Firmware

I offer a service to upgrade the PolarStar Fusion Engine Firmware, but for those that would like to upgrade the FCU firmware themselves, here are the instructions on how to do it. Please note that PolarStar Airsoft nor Bingo Airsoftworks can be held liable if you damage or destroy your FCU by attempting to update the firmware. Please proceed at your own risk.

To update the FCU firmware, you’ll need the following:

  1. IMG_2215Purchase/acquire the AVRISP mkII programmer and download and install the Atmel Studio 6 software
  2. Plug the programmer into a USB port on your computer. The light on the programmer should be red.
  3. IMG_2213Carefully remove the heat shrink covering from the FCU. It’s easiest to cut on the edge of the circuit board with a razor blade.
  4. Insert the 6 pin connection header into the connector on the programmer.
  5. IMG_2216Attach the programmer to the FCU and hold in place using a clip or rubber bands. Make sure the red line on the data cable lines up with pin 1 on the FCU circuit board programming jumper pad (pin 1 has square solder trace)
  6. IMG_2217Attach a fresh battery to the FCU. The light on the programmer should turn green.
  7. fcu_firmware1Launch the Atmel Studio 6 software and access the Tools | Device Programming menu.
  8. Make sure the Tool drop down reads “AVRISP mkII”. Make sure the Device drop down reads “ATmega169A”. The Interface field should be “ISP”. Then click Apply.
  9. Click on Device Signature Read button, and a device signature and Target Voltage should be displayed.
  10. fcu_firmware2Click on Memories option in the left column.
  11. Backup the existing firmware by clicking on the “Read…” button. Enter a file name and accept. The programmer will read the current firmware and save as the file specified.
  12. In the Flash (16KB) field, enter or navigate to the path of the new firmware .hex file from PolarStar Airsoft.
  13. Make sure “Erase device before programming” and “Verify Flash after programming” are checked.
  14. Click on the Program button to program the FCU. The light on the AVRISP mkII programmer should turn orange while programming.
  15. Disconnect the battery from the FCU, disconnect the FCU from the programmer.
  16. Important: Reset the FCU (hold the settings button down while plugging in the battery) and then verify that the firmware revision is correct (most current is re22)
  17. IMG_2211Reapply heat shrink to FCU. Punch a hole in the heat shrink for the select switch before heating and shrinking.

Happy Airsofting!

– Rudy