Since the PolarStar Fusion Engine came out, I’ve wanted to build a Fusion Engine powered M14 (and several people have also asked me if it was possible). I’ve been mulling about on the idea for some time knowing that the M14 uses a V7 gearbox, the nozzle is significantly offset, and there is hardy any room in an M14 body. I picked up a boneyard M14 and finally decided to try and figure out a way to make it all work. It was a pretty significant challenge, but in the end it all came together and the Fusion Engine actually works quite well in an M14. It required some serious hacking away at the V7 gearbox shell to provide a cradle for the Fusion Engine and to maintain the trigger and safety functionality. It also required the fabrication of a new nozzle extension and milling on the front cylinder of the FE. I also had to remove the wire guides from the back of the Fusion Engine, to make room for the air line. The one external feature of the M14 that I could not maintain was the fire selector switch. Since the V7 gearbox had to be cut up to hold the Fusion Engine, the support for the selector switch had to be removed. I replaced the selector switch with a slide switch, which actually makes it easier to use, but of course, its not 100% externally correct. Nonetheless, below are the pictures of the work that was done to convert the AGM M14. There are a few changes I would make if doing this conversion again, specifically I would simplify how the FE is bolted to the the gearbox cradle, and I plan on using special 90 degree elbows for the air line instead of bending it. To do this conversion I used a blank front cylinder from PolarStar. I had to mill it and drill the vent holes and nozzle air line attachment points. Now that I know what needs to be done, the modification would be easier on a stock FE front cylinder.
I will be field testing this gun very soon. It has performed flawlessly in my workshop/backyard testing so far. This boneyard gun had a lot of other problems (several broken parts, right out of the box), so I’d like to see it in a “complete” M14. I’ve also examined an EBR up close, and I think I could now do this conversion to the EBR, just not sure if anyone wants me to hack up their gearbox shell on such an expensive gun! 🙂 Well, having the Fusion Engine powering the gun, I think it would be well worth it!
UPDATE (24 May 2012):
The M14 conversion now retains the use of the stock trigger switch. This allows the “feel” of the M14 trigger pull to remain the same. Also I added a set screw to the top nozzle instead of simply gluing it to prevent it from shaking loose from the bracket.