1911 Gunsmithing: lower and flare ejection port

1911 Gunsmithing: lower and flare ejection port

Over the past two decades or so, lowered and flared ejection ports have become fairly common on 1911 pistols. Occasionally, you’ll encounter a pistol made to original 1911 specifications (or close to them) that you may want to lower and flare.  In this post we’ll work on my Auto-Ordnance 1911BKO (to learn more about the 1911BKO, click here).

Lowered and flared ejection ports are typically associated with increased reliability.  This may be the case, but it is worth noting this pistol has been extremely reliable right out of the box.

For reference purposes, a schematic of the 1911 pistol can be found here.

Anytime you work on a 1911, the Kuhnhausen Shop Manuals are worth their weight in gold.  If you even have a passing interest in 1911s, buy a set; they are filled with information, history and drawings.


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Any modifications made to a firearm should be made by a licensed gunsmith. Failure to do so may void warranties and result in an unsafe firearm and may cause injury or death.

Modifications to a firearm may result in personal injury or death, cause the firearm to not function properly, or malfunction, and cause the firearm to become unsafe.

This is what the slide of the AO 1911BKO looked like from the factory.  Note there isn’t a flare on the rear edge of the ejection port cut and the side of the port is quite a bit higher than most you’ll commonly encounter on contemporary guns.

For this slide, I’ll make all of the cuts on the milling machine.  Flaring could easily be accomplished with a hand held rotary tool and an abrasive cone.  Lowering a port could probably be done with hand tools, however, I think this would best be left to a milling machine.

I’ll be using the following tools from Brownells for this project:


There are a number of ways to hold a 1911 slide in a milling machine.  Sometimes I’ll use some hold downs on a pair of 1-2-3 blocks; however, using a Yavapai 1911 slide holding fixture (above) is much easier.  The slide fits onto the aluminum fixture and is retained with two cap screws.  The fixture allows the slide to be set up fairly easily in the milling machine’s vise.

The top and bottom of a 1911 slide are not parallel.  As a rule, machining on the top half of the slide, should be parallel with the top (French cuts for example, however, sights are not).  In the case of the ejection port, it should be parallel with the bottom of the slide.  Since the milling machine’s vise is parallel to the X-axis of the machine, I can simply clamp the fixture with the slide in the vise and have a workable set up.

Machining a cut like this is fairly easy with the help of an edge finder (above) and a digital readout on the mill.  First step it to locate the bottom edge of the slide, and front and rear of the ejection port.  The edge finder is .200″ in diameter, when it touches the edge of the work piece, it moves off center.  This location would be .100″ from the edge.  From here you can calculate your cuts.

I’m using a 3/8″ 4 flute solid carbide end mill to lower the ejection port.  Some guys use 1/2″, some use 1/4″; each will give a slightly different look.  I cut down until there is .450″ worth of material left on the bottom (Colt Gold Cups are .475″, some guys cut down to .430″).

Now I need to relieve the inside edge of the ejection port.  I used the same 3/4″ end mill with the slide re-positioned in the Yavapai fixture.  I located the front and rear edge of the slide, centered the DRO and machined out the cut above.

There are a number of methods and styles to flare an ejection port.  I decided to use a 3/4″ ball-nose end mill with the slide firmly positioned as shown above.  Using a set of 1911 Auto ejection port grinding stones with a rotary tool would also work well.

Passes are made .010″ deep at a time.

And this is what the slide looks like now!  Ready for the next step!

Read our review of the Auto-Ordnance 1911BKO here.

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