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.

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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.