The included endcap and pic rail files don't line up properly and you have to drill out the hole to get it to work.
I'm just learning how to model so I don't know how to just move the hole but I spliced the two together to eliminate the need to use screws.
I printed and replaced mine and it feels a lot better, it sits and looks better too.
Printed side plates for the DB9-22
UMP 11-9 Release Pack HELLO KITTY
UMP 11-9 silicone buffer pad mold