“What’s this notch below the dust cover on my HK416?” the question we've been constantly asked by the users of other brand's products since they have launched their HK416 kits as well. The shocking question just recalls my memories and makes this small notch a big reflection of the knowledge of manufacturers.
In the beginning, when we started to develop our 416 receivers in winter of 2014 we had taken some airsoft spec HK416 as our references, and we found out the mystery 3mm x 7mm notch just below the ejection port on the airsoft 416. We followed same design on three or four receivers but removed the notch in contingency due to the fact that we found it’s tremendously off spec and does not exist at all on the RS HK416 upper.
You could tell from the photo above: among of them (HK416,MR556, ), none of which have the notch.
After the success on our 416V2, we finally have the time to do some research on "the notch", why they drill this notch under the port? The answer is unclear until we bought the RS HK416 dust cover from Germany; the dust cover is the main reason why they have the mystery notch on their uppers.
The interference between the dust cover and upper will cause the closing malfunction. It seems that airsoft company made some R&D mistake when they molded the polymer dust cover. In order to make the port closed properly, I assume they have to drill this mystery notch to avoid interference, it’s quite a common way in the market; besides, the notch is usually covered by the dust cover, or they did this to make it compatible with their 416 GBBR version. Well, that’s another question we need to look into.
You could easily tell by the 3D scanned plan that The RS HK416 upper doesn’t have the notch below the port due to the fact that its dust cover wouldn’t interfere with the upper when it's closed.
Again, we have to claim that this notch stuff normally occurs on the industrial R&D fixture plan but the thing that still confuses us is that why our competitor cloned the R&D fixture plan from the airsoft company and claimed that it is MILSPEC. Then i have to blog this as an annoucement for having a notch is not a Milspec story to wave as much as question about notch from their customers.