With the anouncement of the RA-Tech DIY Challenge Pack for the GHK M4 GBB, RA-Tech posted a video showing a GHK M4 GBB already upgraded with the pack. This is a challenge for those who prefer to build their own gas blowbacks with premium parts on the heavy kick GHK M4 GBB.

More photos of the Challenge Pack at the RA-Tech Facebook Page.