This some sort of Private/Sentinel clone correct?
If so theres a decent chance the pin is actually floating, ie it should move inside the delrin insulator, but its just crazy (too) tight (not uncommon on these).
Take off the mods top, set it on something circular (hole in middle) and lightly tap the pin inside the 510 i'd be willing to bet it starts moving down. Then flip it over and tap the other way and vice versa and it should loosen up and start to float properly.
Also always tighten down the atty on the mod before you tighten up the telescopic.
Best of luck!