How to convert the VFC HK416 GBB upper receiver to suitable for the PTW

2018/05/23 First version
2019/01/05 Updated

Hello everyone (´-` )/

 There are many conversion kits of HK416 PTW. For example, HAO and nborde develop the kits for PTW markets. Of course, these are very high quality but unfortunately, I am not rich man so these conversion kits are expensive for me. That means there no choice without making a converted HK416 upper receiver.
 Fortunately, I can afford VFC and WE genuine receiver parts for HK416 GBB rifles in Japan. I had tried modifying them and succeeded ;) The modification is relatively easy for me.

■Required Tools■
Each examples are in parentheses as references. The milling machine can be substituted by the leutor or files

1. Drill (SHINKO ACD-280)
1. Grindstone with shaft φ
2. Extension shaft for drill
3. Flex hone (YANASE KENDAMA KTM-29-SC-60)
2. Leutor (DREMELL 4000)
1. Sanding band
2. High speed cutter φ3
3. Milling machine (PROXXON No. 27000)
1. End mill φ6

■Step1: Expanding inside diameter of the receiver
　The most important step is expanding inside diameter of the receiver for PTW cylinders.  The VFC HK416 GBB receivers are made by aluminium die casting. That means the upper receiver has rough shape and diameter. In addition the diameter about φ24.5 at minimum that means it is too small for the PTW cylinder assembles.
 At first, I tried rough machining by the grindstone with shaft which was extended by the extending shaft which was attached into the electric drill. This machining was very rough removal process which was conducted in a bucket which was filled up water. A good reasons for using water are cooling grindstones and prevention of scattering of cutting powder. In the process, only some specific places will be removed but that means succeeded. Because, the first process expand some specific places which are particularly small inner diameter.
 Secondly, I switched the grindstone into the flex hone and grinded whole inner shape of the upper receiver as shown in Fig.1.

Fig.1 The upper receiver after expanding inner diameter.

■Step2: Additional Expanding inner diameter for stepped inner diameter shape for PTW cylinders
 SYSTEMA and other clone type cylinders have stepped outer shape as shown in Fig.2. That means you have to expand inner shape of the receiver more 0.5mm as diameter.
 I used the leutor with the sanding band to expanding the inner diameter. The process is grinding a recess shape therefore, you can use rough machining tool.
 If you have FCC type smooth outer shape cylinder, you can skip this process.

Fig.2 Spring gude side outer shape of SYSTEMA PTW cylinder

■Step3: Adding locating notch for a PTW cylinder

 TW type upper receivers have a locating notch at a takedown pin block to hold the cylinder position. The notch has 4.5mm width and 10mm depth. You might think that "That is difficult process to add the notch!" but it isn't. Don't worry.
 I used the leutor with the high speed cutter ∮3.0 for this process. At first, I milled rough shape notch on almost center of the takedown pin block. Positioning was just checking by my eyes. Then, I expanded the notch width to 4.5mm and digged to 10mm depth. If you miss notch position, you can revise the notch position until this expanding process.
 The result as shown in FIg.3

Fig.3  The result of adding the locating notch for a PTW cylinder

■Step4: Cutting ribs for avoiding collision with magazines
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HK417 PTW Project/Motor modification

In this page, instructions of the PTW motor modification to fit to PTW HK417 is explained.

■OVERVIEW■
 Lower receivers of the PTW M4s have mechanical structure for fixing a PTW motor. However, of course, the VFC HK417 GBB dose not have one.  Therefore, you have to design and make a motor mounter for the PTW motor fixing into the VFC HK417 GBB lower receiver.

■STEP1: VERIFYING PROBLEMS TO FITTING THE PTW MOTOR INTO THE VFC HK417 GBB■
 Lower receivers of the PTW M4s have mechanical structure for fixing a PTW motor like as Fig.1. However, the lower receiver of the VFC HK417 GBB dose not have one.  Real AR rifles and M4 GBB rifles have a grip mounter in this spot, so you think like that "Is solution additional machining of holes and a slot?". Unfortunately, it is not (; 'A`)

 

Fig.1 Mechanical structure of  the PTW M4 for fixing the PTW motor

  A critical problem is that the lower receiver of the VFC HK417 GBB has an detachable grip mounter as shown  Fig. 2.  This grip mounter has three screw holes. One hole is used for fixing a grip. Other two screw holes are used for fixing itself into the lower receiver of the VFC HK417 GBB. Latter two screw holes interfere in spring pin holes fixing the PTW motor.  That means it is inappropriate for the lower receiver of the VFC HK417 GBB to additional machining.
  A solution of this project is modifying the PTW motor base. That means developing a new motor base integrates the PTW motor base and the grip mounter of the VFC HK417 GBB.

Fig.2 The Grip mounter of the VFC HK417 GBB

■STEP2: DESIGNING THE MOTOR BASE■
 As the solution of the problem, I had designed a new motor base as shown Fig.3

Fig.3 The new motor base for HK417 PTW

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