1911 80% Tactical Machining Build, Part 6: Barrel Seating

Quickly learn how to barrel seat your 80% 1911 build.


Should be the same as cutting the slide rails in Part 5.  Load up the 18mm ball end mill.  You’ll be going for .08″ deep of a cut.  Disclaimer!

1911 80% Barrel Seating
1911 80% Barrel Seating


It was difficult to see where exactly was the middle, so I Dykem-ed  and used the calipers to cut a middle line on the flat area.

1911 Barrel Seat Dykem
1911 Barrel Seat Dykem
Eyeballing 1911 Barrel Seat Cut
Eyeballing 1911 Barrel Seat Cut

I got a good first hole.

Barrel Seat First Cut
Barrel Seat First Cut

But after unsuccessfully trying to mill using the drill press (it walks A LOT), I decided to just go to touching holes.  This is the not very clean final product.

1911 Barrel Seat with Drill Press
1911 Barrel Seat with Drill Press

After some filing and sandpaper, it looks a lot better.  The barrel sits fine too.  I’ll file some more afterwards.

Almost Finished Barrel Seat
Almost Finished Barrel Seat

Keep the jig on and we’ll finish the frame with the hammer & sear pin holes next.

Next Lesson

Part 1: Intro (Finding the 80%)

Part 2: Tools

Part 3: Parts List

Part 4: Basic Fitting

Part 5: Cutting the Slide Rail

Part 6: Barrel Seating

Part 7: Hammer & Sear Pin Holes

Part 8: Fitting the Slide

Part 9: Assembly & Fitting

Part 10: GunKote Application


  1. Did your end mill have a straight shank? Finding the 18mm ball end is really big and doesn’t fit normal chucks. I think most just top out at 1/2″. Did you find a bigger chuck or a mill with a narrower shank?

  2. Eric- Great tutorial! I am getting ready to cut the barrel seat, and at center line I thought I needed to cut down .077″ to the final depth for the barrel seat?

  3. Eric, love your article, it is very informative. However, I have to say one thing.In my opinion, none of the drill presses you mentioned or discussed will accept the 18mm ball nose end mill. I am certain because most drill press chucks do not allow for sizes exceeding the 1/2-3/4 inch bits, and most manufacturers do not allow for the provision of swapping out the chucks for one that meaty to accept an 18mm bit. I fear one would have to go all out and buy an full on industrial Drill Press to accept one. I searched everywhere to find a reduced shank 18mm Bit, and the most all of them had to offer me was an 18mm Ball nose end mill on a 16mm shank. I think one of the possible prospects would be to take the 18mm ball nose end mill to a machine shop and have them machine the shank so that a standard drill press could accept it. Thanks in advance for your feedback on my response to your great article.

    But, I have to inquire, would it not be just as easy to utilize a Dremel tool, and with the time and lots of measurements achieve to barrel seat cut?

    1. Thanks for your comment! Never thought of taking the 18mm ball nose end mill to a machine shop so it could accept it. Let me know how it goes if you decide to go that route.

      In regards to the Dremel tool…it should be doable although I would probably recommend getting a curved file and going slowly while measuring and fitting with the barrel if you’re not going with the end mill.

  4. I also had problems with the depth and chattering when using the ball nose end drill bit. For those of you who are doing multiple builds I recommend purchasing a barrel seat cutter. Matrix Precision Parts sells one for $59.00 (plus tax and shipping depending on your location). It is a jig that fits on the top of your frame and cuts the barrel seat horizontally instead of vertically. The result was perfect. All I needed to do was sand and polish the seat and the barrel fit without any additional modifications.

  5. I was going to ask ( suggest) whether changing the position of the barrel seat cut might help. Cut (grind or file) parallel (to the top and rails) instead of perpendicular.

    I see Matt mentioned a jig that might do the same type of cut as what I was thinking of, before knowing of a jig.

  6. Eric,
    Which 80 percenter was easier, less expensive and most practical and/or trust worthy to build?
    The Glock 80 percent or the 1911 80 percent?

    1. For sure the Glock 80…I’d estimate my 1911 took 40 hours the first time while I’ve heard the Glock was a fraction.

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