You need to be careful if you let it go down to 50bar mate - the rifle will usually piss out all it's air at that pressure, and then you'll have to fill up from zero bar! lol
I would suggest you let the pressure fall in use to about 110 - 120bar, and then fill upto around 180bar (yep, 180bar, not 190bar). I say 180bar because that is the top end of the 'sweet spot' for me. I count 90-100 shots, and then i refill to 180bar. I count my shots because the S310 does not have an on board pressure guage (i thank God ),
Regards,
Grim.
Wise words