Updated: Sep 14, 2019
Had a good question about fitting upper radial lugs on a barrels. Here is an illustration of total aggregate vertical tolerance stack on a 1911. These numbers are very important when you want to achieve a 100% vertical lock up while maintaining close to original blueprint link arc. These numbers are also very important when selecting components. Frames at 0.225" or 0.230" and Slides at 0.845" or 0.850". You want to match 0.225" frames with 0.850 slides and 0.230" frames with 0.845" slides to hit the 1.075" tolerance stack. Barrel upper radial lug slot depth becomes a more or less fixed dimension at this point as well as the radius it is cut at to match the 0.700" diameter of the barrel tunnel, offset 0.302" from the center of the bore. Firing pin location has to be moved to 0.280" lower than the radial lug vertically to accommodate this which some slide manufacturers today are doing this. This is another reason why I really have no interest in rebuilds these days because these numbers are all over the place, most interesting though is why? Another reason I have adopted a build to print philosophy instead of the age old build to fit methodology, math makes more sense than guessing. ***disclaimer*** image is just a quick model, not representative of actual dimensional interaction, the upper lug should come in full contact with the first lug recess of the barrel.