Why? The rear sight will probably not be at the proper height to line up with the front sight, you'd have to make a custom front sight to get it to line up, not to mention that the gas tube wont line up either as the hk416 piston and oprod are higher, which is why the rail height is higher then a typical AR. it would end up being a DI AR on a 416 lower with a 416 rail. Be aware that you may have trouble with the barrel nut off as they are different. but if you want to see what it may look like after, I did a quick and dirty for it, it doesnt look too bad but still makes no sense to me but to e