It seems like Williams Firesights #70231 are not compatible with Pro-Target sights on Buckmark. Front sight is much taller than original. Rear sight is about the same size as original. As result rear sight goes out of range of motion before it is zeroed in rendering sights useless. Pro-Target sights are used on almost all new non fiber optic Buckmarks models.

 

Too bad I did not stop right after I saw it and installed everything. Even threw away packaging. $50 down the drain

 

I did not want to call Williams Firesights at first (because most reviews said support is useless and rude) but then decided that I have nothing to lose. They suggested that maybe they packaged wrong part and asked to send it back for research. Fair enough.