Star SU is currently involved in process improvement for machining the Upper Rail system for AR-15’s, AR-10’s and M-4 carbines with several independently owned contractors. Process improvement includes:

• Concentricity improvement (TIR) critical to non-critical bore
• Cycle Time Reduction
• Surface finishes of Ra ≤ 0.8

Typical current process:

• Rough Drill
• Ream non-critical bore
• End mill critical bore by interpolation

The failure mode for this process is mismatch between the critical and non-critical bore resulting in possible failure of the bolt to barrel interface in field use.

Star Process #1:

• Rough drill using Single Flute Gundrill
• End pilot for SRT Reamer
• SRT ream non-critical bore
• End mill critical bore by Interpolation

The SRT’s ability to maintain position through the reaming process of the non-critical bore results in

TIR ≤ 12µm

Star Process #2:

• Rough drill using Single Flute Gundrill
• End mill SRT pilot and interpolate critical bore
• SRT ream both critical and non-critical bores from one side

With Process #2 cycle time can be greatly reduced, by employing the SRT and reaming from the critical end first. Overlapping tolerances allow for an upper with no step or mismatch whatsoever. Also, by sharpening the rear of the SRT we can ream in and ream out insuring clean-up and a nearly perfect round hole.

Gary McCarel, Application Engineer

Visit us at the Shot Show Supplier Showcase in booths S1833 (Star SU) and S1332 (H.B. Carbide)