SI folding brace break-in DIY
I just got a Kuna and while I like the gun, the Strike Industries l folding brace mechanism drives me nuts. Factory new it is ridiculously stiff and hard to fold in/out, and you can feel the rough machined parts grating together. On day 3 of ownership I took it apart and figured out what needed polishing and clearancing.
Disassembly is as simple as removing the C clip from the hinge pin with a small flat screwdriver.
The first issue was noticable right away - the hinge pin has a rough grooved lathe texture which should have been factory polished. I spent ~15min with some progressive grits of sandpaper, finishing at 1000 grit. The smaller diameter of the pin is easy to do by hand, but I realized the top thicker diameter was more important to be smooth but harder to do by hand, so I chucked it up in my drill and let it spin the pin while I held the sandpaper stationary. I took care not to sand the top or bottom of the pin and it still looks factory when installed.
The pin polishing along with some silicone based brake caliper grease helped a ton to reduce the force needed to unlock the brace, but it was still impossible to pull the brace open with one hand.
When stowed, there is a cam design which technically if forced hard enough would force the brace upward to unlock. I took a metal file to the steep angled cam surfaces (pictured) to decrease the angle and round the edges. The spaces are tight and it's somewhat of a delicate operation, but I managed not to scratch it up too bad. The key here is test often because you can't put metal back.
I can now pull the brace open easily with one had with moderate force and it opens smooth as butter. Closing it is easier although is still locks in pretty tight.