The spring loaded filling is in the 510 itself, when you remove it and fit the bf 510 pin it removes the option to use the spring loaded filling...Thank you, I thought as much.
I asked as the entire 510 pin is rotating in the socket but neither going further in or coming out.
I thought there might be some unlocking required perhaps with the spring loaded filling hole.
Unfortunately it appears now that it could be cross threaded.
Knew i’d end up with a dodgy eBay but one day.
B,
S.