I managed to purchase for my self an ACOG EREK cantilever adapter.
Now to be honest, I’m not exactly sure what EREK stands for. I’m guessing something like Eye Relief Extension Kit.
So why did I buy it? Because I wanted one. Some time back, I saw some pictures of the USMC trying a cantilever mount for the ACOG on the M16A4. Since them I have wanted to give it a try.
When you read about people complaining about the ACOG, the first complaint is always price, the second tends to be about the short unforgiving eye relief. Once you take that short eye relief of the ACOG and have to mount a BUIS behind it, combined with a fixed stock, it can be annoying. Personally, not only have I gotten used to it, I am rather fond of the ACOG mounted forward as I shoot nose to the charging handle.
So at some point the USMC had some adapters made up that moved the ACOG back and over the Knights 2-600m rear sight. This makes the ACOG easier to use with the A2 fixed stock. Now I tried to find pictures of it in use again, but I was unable too. My guess is that the USMC tested it and for what ever reason decided not to use them.
Why? I don’t know. Perhaps raising the ACOG up make it more unacceptable to damage or abuse changing the zero. It might not have been worth the cost. Or someone might have come to their senses and said use the M4 instead. In any event, I have one to use now, and it is rather nice. It lifts the ACOG up enough that the charging handle is easily accessible, and moves the ACOG far enough back that you don’t need to crane your head forward for nose to the charging handle.