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

The Silver III design comprises four parts:

1.  Fire control group receptacle (FCR)
2.  Grip boss and stock tower (GST)
3.  Right magazine well (RMAG)
4.  Left magazine well (LMAG)

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

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.  There is a sliver of material removed from the left wall of the FCR that is part of the magazine release lever cavity milled in the LMAG.  This can be a through hole of any diameter larger than the width of the cavity instead of the current feature, which is unnecessarily difficult to machine.

4.  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.

LMAG 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
