HK 416, R556 Castle Nut - A5 Style - Extended

I put this on a Vltor A5 extension. At first it felt like the thread pitch was wrong and it would not screw on the extension. But as I worked it back and forth it started to screw on. Heavy coating on the two parts looked to be the problem. Took some time to mate the parts but they fit and I got the HK look with the castle nut, and HK pistol grip and HK stock on my SIG 516. Thanks HKParts.

This newer version of HKparts' HK416a5 style castle nut is the same length as the original HK, though it seems to be melonited/nitrided rather than the phosphate/parkerized coating HK uses. In this way it is very similar to the one HK Haus produce. I say newer version because the last one I purchased from HKparts, while extended when compared to a regular castle nut, it was not the full length of the genuine HK piece. While it's nice that this newer one has the full dimensions, it does make it more difficult to fit on certain buffer tubes, depending on what end plate you choose. The picture below has the castle nut purchased for this review with a qd socket end plate, a free standing regular castle nut, and the older style of HKparts castle nut shown above the newest version.

great upgrade to the standard castle nut one finds on other AR-15 types. This one is about 5/8 of an inch long whereas the standard one I have on another of my rifles is just under 3/8 of an inch