Project of retractable stock suitable for VFC G3A3 GBBR

■Background

 The VFC G3 GBBR is nice quality airsoft rifle but it has few optional aftermarket parts for customization. Especially, stocks and grips!
I found extremely cool design rifle stock is Spuhr R-410 but I can not import that into japan because ITAR regulation.
So, I determine that design similar retractable rifle stock for the VFC G3 GBBR.

How to convert VFC M4 bolt carriers suitable for WA M4 GBBRs

■Background■

 Recently, I fascinated WA GBBRs. An unique advantage of WA GBBRs is variation of outer aftermarket parts. However many aftermarket parts are discontinued especially, internal parts. So I have to find out alternatives.

■Required Tools and chemicals■

 Special tool or chemicals I used as follows. I think that the milling machine can be substituted by a leutor or files but I recommend using a milling machine.

1. Milling machine (ex: Proxxon No.27000 or better)
• ∮6.0 mill
2. Leutor (DREMELL 4000) 
• High speed cutter φ3
3. BIRCHWOOD Aluminum Black Metal Finish

■STEP1 Cutting down a valve locking notch■

Note: Especially, dimension of VFC bolt carrier is same as same real AR rifle bolt carrier. that means you have to use "real size" receiver or cut out back side of the VFC bolt carrier for the converting.

 Major difference between VFC genuine bolt carrier and WA's one is valve locking notch. The WA bolt carrier has a notch on bottom of the bolt carrier but VFC one does not have the notch as shown in Fig.1.

Fig.1 difference between WA type bolt carrier and VFC type one

 Dimension of the notch is shown in FIg.2. There are two slopes in front and back side of the notch. However, I believe that important dimension is length of flat surface. Because, a role of the slopes is realization of smooth moving of the valve control linkages on magazines. 
 I milled flat the flat surface by my little milling machine then, I added the slopes by the Leutor.  The result is shown in Fig.3. 

Fig.2 Dimension of the valve locking notch

Fig.3 Added the valve locking notch on the VFC bolt carrier

  After finishing modifying shape of the bolt carrier, you have to do firing test of your rifle with the converted bolt carrier. In my experience, I had to do some additonal modifying as follow sections.

■STEP2 Adding chamfer on a edge of a lock part■

 In current case, the VFC bolt carrier collision with a bolt catch. That means my rifle with the converted bolt carrier holds open after every shot even driven by full loaded magazine.  This process is not necessarily required for the converting of the VFC bolt carriers. I believe that this problem ocurred by some part dimensions of a firing pin block.
  Therefore, you have to check necessity of this process using your rifle with the modified bolt carrier after STEP1.

Fig.4 The lock part with chamfer (red circle) in front of the bolt carrier

■STEP3 Expanging inner diammetor of a  bolt carrier key■

 Usually, WA type GBB rifles have slightly shorter gas tube than real one. Thus, the WA blot carrier have bolt carrier key without hole which connects to the gas tube. the VFC bolt carrier has a bolt carrier key with slight small and shallow hole as shown in Fig.5.

Fig.5 The bolt carrier key on the VFC bolt carrier

 My rifle has longer gas tube (Fig .6) than WA genuine one. Even the VFC bolt carrier key collisions with the gas tube. That means more large and deep hole of the bolt carrier key is needed.
　

Fig.6  Longer gastube than WA genuine one which installed in my GBB rifle

 A solution is easy. That is just drilling! I used ∮4.8 drill and digged roughly 20mm depth as shown in Fig.7. As the result is shown in Fig.8. However if you adopt a "more realistic" gastube,  you have to expand the hole further more.

Fig.7 Drilling the bolt carrier key with a ∮4.8 drill

Fig.8 The modifyed bolt carrier key

■Conclusion■
 Finally, I finished converting the VFC M4 bolt carrier suitable for WA rifles. I satisfied the result because the converted bolt carrier works perfectly.