Air Assault is a local field for me and I actually talked to Brent, their tech who did this with his Geo and I believe made this one also.
It is a cut off and aluminum weld job.
It sounds like there are some issues with this though in that the aluminum used to weld causes issues with the anno and "eats" the anno, and eventually the weld will fail from my understanding. If you are really interested in more on how this was done specifically you could PM el Pengo (Brent) and maybe he'll share more info.
It doesn't look perfect but it doesn't look too bad either, especially considering how it was likely done.
I don't understand why people are failing to comprehend the point of doing this; it makes a lot of sense. I can imagine being able to grip the frame with the additional help of your middle finger would stabilize your shots a whole lot more, as opposed to just sort-of having that finger float above a double trigger. Since these markers run on ramping anyway, it makes perfect sense to me...
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Mechanical Engineering 2012