Installing McMillan flush cups for quick-detach slings

The McMillian flush cup (left and center) is threaded to allow height adjustments. A traditional flush cup (right) does not have this feature. The bottom of the McMillian flush cup has an allen key cut out to allow the installer to thread it in or out. The opening also allows excess epoxy to escape from behind the cup during installation.

Quick detach, flush mounted sling cups offer the shooter easy attachment and removal of a sling while remaining unobtrusive and snag free on the rifle stock.  Unlike a traditional QD stud, flush cups are below the surface.  For instance, when located on the bottom rear of a stock, a traditional stud can drag on a rear bag, with the sling removed, the flush cup does not have this problem.

For this project we ordered the following items from Brownells:

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On this stock will be installing flush cups on the bottom front, bottom rear, left front and left rear of the stock.  Our stock already has traditional QD studs in two of these locations.  The traditional QD stud is removed from the stock.

On this stock will be installing flush cups on the bottom front, bottom rear, left front and left rear of the stock. Our stock already has traditional QD studs in two of these locations. The traditional QD stud is removed from the stock.

With the stock secured on the milling machine in a vise, a 9/16" center cutting end mill is used to drill a recess to house the flush cup.

With the stock secured on the milling machine in a vise, a 9/16″ center cutting end mill is used to drill a recess to house the flush cup.

We use a vacuum to remove the epoxy and fiberglass shavings from the stock.

We use a vacuum to remove the epoxy and fiberglass shavings from the stock.

The McMillian flush cup (left and center) is threaded to allow height adjustments.  A traditional flush cup (right) does not have this feature.  The bottom of the McMillian flush cup has an allen key cut out to allow the installer to thread it in or out.  The opening also allows excess epoxy to escape from behind the cup during installation.

The McMillan flush cup (left and center) is threaded to allow height adjustments. A traditional flush cup (right) does not have this feature. The bottom of the McMillan flush cup has an Allen key cut-out to allow the installer to thread it in or out. The opening also allows excess epoxy to escape from behind the cup during installation.

The hole is coated with Marine-tex epoxy and the stud is adjusted flush to the surface.  Any excess epoxy is cleaned from the area.

The hole is coated with Marine-Tex epoxy and the stud is adjusted flush to the surface. Any excess epoxy is cleaned from the area.

The front left and bottom left studs.

The completed front left and bottom left studs.