Silver Revision IV: AR-15 lower receiver assembled from extruded aluminum parts.
October 2015

The Silver IV design comprises three parts:

1.  Fire control group receptacle (FCR)
2.  Grip boss and stock tower (GST)
3.  Magazine well (MAG)

All three parts are machined from extruded stock, and all three require considerable machining.  Minimizing the machining necessary will be a focus of subsequent design revisions.

Silver IV differs from Silver III in the follwoing ways:

1.  The magazine well is now a single piece instead of two halves screwed togther.  The magazine well attached to the FCR in the same way the two halves did with Silver III.

2.  A modification has been made to the geometry of the magazine well where in meets the FCR.  In Silver III this feature would have been difficult or impossible to machine.

3.  A modification was made to the FCR expanding the cavity for the rear of the magazine catch lever to make it easier to machine.

In all other respects Silver III and Silver IV are identical.


FCR KNOWN ISSUES:

1.  While the FCR extrusion includes a cavity to accept the GST, more material needs to be removed from the final part to accept the fire control group components.  This operation requires a mill.

2.  The FCR engages the magazine well parts with a complicated stepped contour that requires a mill.

3.  The trigger guard opening is smaller than a standard AR-15, to make room for fasteners.  Only four #8 cap screws at two locations secure the FCR to the magazine well parts.  There does not appear to be room enough for more fasteners.

GST KNOWN ISSUES:

1.  All cuts for this part are from the side, with a mill of maximum diameter of 0.10 inch.

2.  A hole and 1/4-28 thread needs to be added to the grip boss at an angle.

3.  The large hole and 1 3/16-16 thread needs to be added to the stock tower.

MAG KNOWN ISSUES:

1.  The bolt release pivot hole is longer than standard.  A standard roll pin can still be used, but it will be difficult or impossible to remove after installation.  An alternative would be to machine threads in the hole and use a set screw instead of the roll pin.


Mitch Barrie
Costa Mesa, CA
mitch@mitchbarrie.net