VIS Dimensions... why generic dimensions don't work.

I often get asked about how far back to cut the VIS on clark/para or nowlin/wilson VIS cuts, and the answer to the question always starts with another question, how far back is your barrel VIS in relationship to the link pin hole? I will start out by saying that I prefer to use Clark/Para barrels, because you can cut the frame VIS and HIS all in one setup for simplicity, accuracy, and repeatability, so for this reason I really like clark/para design barrel VIS. There seems to be some generic dimensions that people like to use for the distance between the slide stop pin hole and the VIS, but generic dimensions only work when the barrel manufacturers all work to the same standard, and I am here to tell you they do not. For example, KKM clark/para barrels run around 0.4935" from the center of the link pin hole to the back of the barrel's VIS (back of standing lug), where KKM barrels run around 0.500" from the center of the link pin hole to the barrels VIS (back of standing lug). This example alone shows a difference of 0.0065" of where the location of the frame VIS should be in relationship to the slide stop pin hole. The barrel is attached to the slide stop pin by the link, which has a fixed arc. The barrel cannot travel outside of this fixed arc so the location of the VIS in relationship to both slide stop pin hole and link pin hole will for most applications, be easily determined based on measuring the barrel. The above illustration above shows the relationship between the original blueprint and a randomized example of a clark/para VIS. As you can clearly see the VIS location simply becomes a relative plus/minus equation based on known dimensions... if the VIS on the barrel is 0.243" further back from the link pin hole center than the standard blueprint, the VIS on the frame needs to be cut back 0.243" further from the slide stop pin hole. For my building purposes I setup a spreadsheet to plug in the numbers to quickly determine the VIS location based on the barrel that I am using. Just another detail to ensure proper timing on 1911s. Hope this helps. If anyone wants to excel spreadsheet just message me.

Next I will dive-in to the lower lug profile and where to stop the cut (slide stop pin abutment).