Here are two more photos shoing the OKC3S mounted on AR-15s.
Note this is a full auto M4A3 with a 14.5-inch barrel and the bayonet ring is where it is supposed to be:
Thanks to hk33k2 of ARFCOM for use of his image above
Note in the following photo this is a 16-inch barrel and the mounting ring is around the barrel instead of the base of the flash hider! Also note the barrel is a smaller diameter then the flash hider so there is a fair amount of slip when mounting a bayonet like this!
Thanks to Ahiodsohi from ARFCOM for use of their image