well, check with greyhaze as their variant may differ.
mine got stuck once...I had the same atty on it day in and day out, and kept it on the mod (with tubes removed) to rebuild.
I took the atty off and had the same as you...went to a basin, hot water, let it soak 10 mins, then used a screwdriver to push it form one side, then back again, then push and so on..just work the sliding mechanism of the top pin
I later found out you could just bang the 510 connector and the whole thing pops out the bottom, making servicing much easier
your mod, may differ..but this is all good for the brass m16 from FT