Updated: Dec 28, 2022
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 and slides are manufactured at two different standards...Frames at 0.225" or 0.230" from the slide stop pin hole center to the bottom of the slide rail raceway, and Slides at 0.845" or 0.850" from the bottom of the rail to the top of the barrel tunnel. You want to match 0.225" frames with 0.850" slides and 0.230" frames with 0.845" slides to hit the magical 1.075" tolerance stack standard. 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. The radial lug recess on the barrel is cut offset to 0.302" from the center of the bore to achieve this standard. So starting with 1.075" minus 0.302" from barrel radial lug recess to center of bore, minus 0.503" from center of bore to center of link pin hole, minus 0.270" from center of link pin hole to the center of the slide stop pin hole, we can see how each of these components are relative to one another dimensionally in the complete assembly. One of the main issues we see today with building 1911s is mismatching these components which can lead into either a +0.005" vertical swing up, or a -0.005" vertical swing down, this is what causes lower lug profiles to vary so greatly in size, and long/short links, or issues with barrel to slide clearance on the low side of the vertical stack. For proper timing on the 1911, you want to be as close to this 1.075" #3 link profile as possible. Too often builders and hobbyist chase these numbers without a full understanding of how they relate, in an effort to identify why something is off. This is a reason why I really have no interest in rebuilds these days because these numbers are all over the place, and to truly have control over the final product, you really need to start from scratch. This is also the reason I have adopted a build to print philosophy instead of the age old build-to-fit methodology, math makes more sense than guessing, dimensional consistency not only creates accurate and reliable guns, it also helps diagnosing issues you may encounter during the build process. I am sure you have heard the old saying... numbers don't lie... and this is not to say other ways of building are inferior, just sharing some good information and the reasons why I do what I do.
***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.