At the end of Part One, I had the two main external components at hand:
The receiver tube and the stock have been roughly cut, so most of the work to do was internal. I designed a custom hop unit to fit inside the receiver and feed the BBs back from the magwell to the chamber.
I sent off the orthographic drawings to a guy who can do 3D CAD work and he converted my designs into a digital model before 3D printing it in ABS. It looks smashing, far better than I ever expected!
A bit of filing was needed to fit the hop in the tube, combined with a light tap with a small hammer and it was seated in place. A piece of barrel sits in the space in the side to engage with the magazine.
The outer barrel is a piece of tube sat in the centre of the cooling jacket. Welded at the front and back are two steel rings to suspend the tube and at the front is the perforated front cap.
Another little tap with the mallet and bingo, it fits very nicely!
The rear cap has a space to take the locking latch, which is sprung with a tension spring. There are two screws in the edge of this back cap to secure it in place, though I may put another in the top.
This latch then locks into the locking unit on the stock.
The rear sight functions much like the original, it is basically a miniaturised version of the sight I put on the MG08/15 with a ramp providing elevation adjustment and the leaf moving left and right for windage.
There comes a point where you have to just try and fit the gearbox! Inevitably somewhere in your designs something will come a-cropper, in this case I forgot to factor in the nozzle position being at the top, not the centre of the cylinder casing. As a result the stock would have to be about 10mm deeper to fit the gearbox. Given that I have already made the stock this isn’t a great option! I plan to get a custom cylinder head made so that the nozzle is in a more convenient place.
Also to save space I have conducted a little modification to the gearbox externals. The motor cage in most V7 gearboxes is angled down slightly to fit in M14 models. This is great if you are building a rifle, not so much for this project!
My first thought was to build a whole custom motor cage but this would be a huge job. Instead I modified the original cage so that it sits slightly angled up. The motor came into contact with the back of the spring casing before it could be secured so a little material had to be removed from there. As you can see from the photo above, the trigger and a part of the fire select has also been removed.
The stock also needed a bit of space cutting out to take the gearbox. The shape eventually had to be quite complicated to take the wire guides on the side.
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Still to come! Trigger unit, gearbox mounting and the magazine housing.