Optimus Defense 80% Billet Lower

As mentioned in the video review of the Optimus Defense 80% Billet Lower that was milled out to full auto specs seen below, I was unable to fit my 100 round dual drum magazine from KCI into the lower. These are a Korean knock-off of the better known BETA mag. As you can see from the photos below, the Magazine well of the Optimus lower is flared. This is a nice feature that allows for a larger target when seating a fresh magazine under stressful conditions. However, the flare of the magazine well adds additional width to the lower and unfortunately interferes with the dual drum design.

The Optimus lower is also somewhat longer than a typical forged lower. This creates a longer path for magazines to travel into the gun when seating. Therefore if the magazine exterior dimensions change such as with the SureFire 60 and 100 round aluminum body magazines, the mag will not seat. The flare of the SureFire magazines hit the magwell on the lower and do not allow these high capacity magazines to seat.

If you would like to see the process for completing your own 80% lower click HERE for my video on the Whiskey Arms 80 percent lower.

This is the configuration we used for most for the testing.  It proved to be the most fun when shooting fully automatic.  The recoil and muzzle flash combined with the concussion from the muzzle break got high marks on the fun factor scale.

This is how I received my 80% lower.  In the photo you can see there is no trigger/hammer pin holes drilled.  Also, the fire control pocket for the LPK (Lower Parts Kit) is not milled.  This makes the lower not a gun by the ATF rules.

Looking at the bottom of the Billet lower, you can see that there is not hole for the trigger.  This is another part of the lower that the user needs to complete in the build process.  Also take not of the enlarged magwell (where the magazine sits).  This will be discussed more in the pictures that follow.

Here is the lower showing the fire control pocket after being milled.  Since a Licensed Class III Manufacturer was doing the machining work to complete this lower, they milled and drilled a few extra locations to allow for the Fully Automatic fire control components.  See the video below for a demonstration of the final result and a closer look at this lower and its parts.

Front view of the Optimus Defense lower with the 100 round AR15 drum magazine inserted as far as it will go.

Optimus Defense 80% Billet Lower (Left) and Typical Forged AR15 Lower from Colt (Right)

Front view of the Optimus Defense Lower with a SureFire 60 Round Mag inserted as far as it will go.

Rear view of the Optimus Defense Lower with a SureFire 60 Round Mag inserted as far as it will go.

Mag catch removed from the lower so you can see how the SureFire double stack magazine does not travel far enough upward into the magazine well for it to catch and fully seat in the lower.