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It's really great that some companies are now putting Picatinny weaver rails on rifle shoulder stocks. The shoulder stock rail could provide more mounting options for your accessories. The should stock rail on the APS ASR107 M4 URX Raptor airsoft rifle is a good example. Because I did not want to use a LiPo battery in the buffer tube, I decided to add a PEQ battery box to the shoulder stock rail. Unfortunately, the shoulder stock rail is a little too short and too far back. If I mount the PEQ box, it would stick too far out back (see photo below).
This shoulder stock used on the APS ASR107 M4 URX Raptor is an OEM part that is marketed by different brands. Matrix also distributes this exact same shoulder stock and is available on Evike's web site.
One option is to replace the short shoulder stock rail with a longer piece. Good thing the shoulder stock rail is not molded into the shoulder stock. It's fastened to the shoulder stock with two screws.
Finding replacement rails that would fit just right is not so easy. Most of the rails on the market has screw spacing that are just two rail spaces apart. But the shoulder stock rail is three rail spaces apart. Luckily, Matrix has a set with a long rail that is three rail spaces apart. The photo below shows the Matrix packaging that includes the long rail.
This package comes with three metal rails. One long one and two short one (see photo below. The two short ones isn't useful for this project, but can come in hand in the future. The long rail will be used to replace the shoulder stock rail. The package including mounting screws.
Putting the long rail on the shoulder stock, in between the short rail and the PEQ battery box, we can see that the longer metal rail is the perfect size for this project. The screw mounting holes are also perfect match (see photo below).
After unscrewing the short rail from the shoulder stock, we find that the short rail is made out of plastic (see photo below).
We screwed the longer rail onto the shoulder stock using the existing screws, rather than the new screws that came with the longer rail. We wanted to retain existing threading that was already impressed into the plastic shoulder stock. The photo below shows the longer rail on the shoulder stock.
Next, we mount the battery box to the shoulder stock. The photos below shows the mounting point and how the battery box looked on the shoulder stock. The battery box and the longer rail is just the right length for this shoulder stock.
This battery box is reviewed here: Cyma C.69 MP5 Batteries Case Review.
Finally, we cut a small notch into the shoulder stock rubber pad to route the APS low-resistance battery wiring from the shoulder stock to the battery box (see photo below).
In this configuration, we can extend and retract the stock without being effected by the battery. Overall, this is a fun and easy modification to perform on our AEG. The hardest part is finding the parts that are just the right length for the job.