I used a Triggertech Special in this build and went to check safety function and realized it was barely engaging. Turns out the safety arm runs into the small shelf in the chassis. It was a simple matter of milling out a small pocket as shown. I’m a jeweler so I had the tools to mill it fairly cleanly but a dremel would take care of it as well.
If you tap the safety a few times to the rear and look at the chassis shelf you’ll see a small white nick where it starts to rub. Just take out 1/4 depth of material from that point to about 1/2 inch rearward and you’re good to go.
1st shot shows the pocket I cut. You can see where it stops in the second photo as opposed to where it should travel to in the 3rd.