I've started working on my first attempt at an Vollmer HK51-B. Most of the RS Vollmer 51-B's seem to have been produced with a synthetic SEF lower, but a few were produced with the 3-round burst trigger group. For this project, I have used a Navy lower from an MP5. I have also used an MP5 cocking tube which has been fitted to the G3 receiver such that the foregrip is at approximately the proper position for an HK51-B. For this first version, I am using a plastic body as practice. Once I can get a hold of a cheap metal receiver and access to some better tools, I'll do version 2. Here is a picture of the work-in-progress.
In order for the MP5 lower to fit the G3, three things must be modified:
-The hop-up unit must move forward a bit
-Some small tabs inside the upper receiver need to be sliced out to let the gearbox slide forward.
-The takedown-pin-tab-thingy at the rear of the lower receiver needs to be replaced or modified such that the G3 stock will properly secure to the lower receiver.
I had to remove the plastic cap off of the barrel-mount inside the upper receiver, and I also had to shorten the plate which holds the hop-up unit inside the mag well. Along with cutting a couple of tabs inside the body, the MP5 lower and gearbox slide forward into position. Here is a picture of the plastic plate that was shortened. As you can see, the gearbox and hop-up are about 6 or 7 mm forward of the original position.
Below shows the back of the MP5 lower, which I have not yet modified. I plan on removing the two-hole mount from the original lower and plastic-welding it to the back of the MP5 lower.
In the following picture, you can see the beginnings of the belt-feed mechanism. This is just taped on for show, and obviously is nowhere near completion.
This modification could also be done for mag-fed G3's, but custom magazines would need to be made due to the new hop-up position. I noticed that the new position lets an MP5 magazine fit on the back-end of the mag-well, so maybe some MP5K mags might work in conjunction with a G3 mag housing.
I'll update this thread as I make progress on the project. Feel free to leave questions, comments, suggestions, or constructive criticism!
Note: The foregrip will not be OD later... I'll be returning it to black, and the inner barrel will be replaced with a shorter one. The flash hider will also be replaced, and I hope to find a sliding stock for it as well. Also, sorry about the pictures, my camera is swimming with the fishes, so I had to use my phone.
