IEBPROJECT CASE STUDY
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A render of a bare aluminium AR-10 lower receiver seen from above at an angle: the open magazine well at the front, the trigger pocket in the middle and a round threaded ring at the back

Machined part designSolo, design and CADDrawing 33 of 47

LR-308
lower receiver

An AR-10 lower receiver I designed myself to the DPMS LR-308 pattern. I drew it to be machined from a solid 6061-T6 aluminium billet, and I wrote a 5-axis toolpath for it in Fusion 360.

Sheet 02 of 05/The part

What the part is

The lower receiver is the frame that the rest of an AR-10 rifle attaches to. This one follows the DPMS LR-308 pattern, which is the common AR-10 standard for .308.

The part is one solid body, so it can be cut from a single block.

A grey CAD-style view of the lower receiver model with black edge lines, seen from the top front corner
PL 04The model with its edges drawn, from the top front corner.
A grey CAD-style view of the lower receiver model with black edge lines, seen from the rear three-quarter with the threaded ring nearest
PL 05The model with its edges drawn, from behind and above, looking into the buffer-tube ring.

Sheet 03 of 05/Material

6061-T6 aluminium, cut from a billet

I drew it in 6061-T6 aluminium. The plan is subtractive, so it gets cut out of a solid billet instead of being printed or cast. 6061-T6 machines cleanly and takes anodizing well. At 2.70 g/cm³ the model comes out at about 350 g.

It'll be cut on my CNC machine once that's built.

A render of the aluminium lower receiver from behind and above, with the round threaded buffer-tube ring nearest the camera
PL 03A three-quarter view from the rear and above, looking into the threaded buffer-tube ring.
A grey CAD-style view of the lower receiver model with black edge lines, seen from below and to the side
PL 06The model from below, showing the magazine well and trigger pocket openings.

Sheet 04 of 05/Toolpath

Simulating the toolpath

This is the first toolpath I've written since the fidget spinner mold. I set it up in Fusion 360 on a generic 5-axis machine, so the part can tilt and the tool can reach each side.

The video below is only a simulation.

A simulation of a grey block being milled into the lower receiver: the tool cuts down from the top, then comes in from each side, and the cut faces turn green, blue and purple by operation
PL 07My toolpath, simulated in Fusion 360. It roughs from the top, then from each side, then switches to a smaller tool for the detail and a thread mill for the ring. Each colour is a different operation.
A side-on render of the aluminium lower receiver: a long body with the magazine well on the left, a rectangular trigger guard opening below the middle and a round ring rising at the right end

Sheet 05 of 05/Takeaways

What I'm taking from it

Gunsmithing is a lot of fun. This lower is one of several platforms I've designed, and right now I'm designing a double-barrel shotgun. I'll keep designing more parts and more guns.

This page only has pictures and a simulation. I'm not publishing the model files or a dimensioned drawing, because of federal firearms law and ghost gun file distribution laws.

PL 02The side profile, rendered in Fusion 360. The magazine well is at the front, the trigger guard opening is in the middle and the buffer-tube ring stands up at the back.