Allen, I'll not be of much help on that M21, but a little note on storing bolt guns in the safe may be helpful.
Every time I clean any of my bolt guns and it's ready to go in the safe, I lift the bolt handle up as if to open the action, then press the trigger while slowly letting the bolt handle down, thereby releasing all spring pressure on the mainspring without dry firing the rifle.
Been doing this drill now for over 40 years, never had a mainspring fail or bind up in any way.
Hope you get all your rat rifles ready for the upcoming assault.....Skippy is out 'n about I'm told as of this week.
Tick-tock......