These modifications have two aspects; one for milling the bolt endcap and one for milling the regulator/ASA. These modifications don't alter the functionality but do serve to customize the marker by eliminating some of the unnecessary material found in those locations.
These modifications might be possible using manual machinery, but it would be a LOT of careful cutting. I'm sure somebody else could do it but as far as I know this type of modification has only been done using CNC.
Bolt Guide Milling:
My first milling attempt was meant to create a very different appearance for the original bolt endcap. I performed this modification on my personal marker, and it turned out good. The downside is that the milling took longer to complete than I was originally expecting. I call this milling the "2 wing" endcap mod because it creates two unmilled wings at the 1-o'clock and 11-o'clock positions.
I went back to the drawing board in attempt to simplfy the modification, with the goal of being able to perform it onto other markers. I came up with a simplification which I call the "1 wing" endcap, because this version is milled from the two sides which creates a single wing in the vertical 12-o'clock position. While this style isn't quite as extravagent as the original 2-wing version, it's much more cost-effective and can actually be done on other markers. The difference is the 2-wing uses a larger tool and has less detail, which speeds up the process.
Relay ASA milling:
This modification is very similar to the "1-wing" bolt endcap milling, where the component is cut from the left and right side to remove a good amount of unused material. This milling isn't necessarially meant to take off all unused material, because that would be very detailed and take more time than I want to spend (the cost would be MUCH higher). The compromise is to make a simplistic design that still removes a good amount of unused material, without pushing the envelope too far. The final part leaves a good minimalist appearance afterward.
Permalink: https://www.youtube.com/embed/7G8KPI159Vg
Simonized Axe:
I searched around while writing this page to find examples of other people performing a similar modification. The best example would be the Simonized Axe which was the precursor to the Inception Axe FLE body style. Simon also milled his ASA in a very similar manner, although his milling is more extensive to remove more material.
(note: the hyperlinks may not work forever)