[jamuke]

you should count out twenty one thousand when filling

or you can zen out and feel the gas exchange,

once you get that solid pfffft and small white cloud of gas when you stop filling you should be done.

it's a silent fill valve so it won't spray like a marui mag
when full
but really you won't overfill or blow a ring,once the pressure in the stock tank and the propane tank are equal the filling stops

you can really tell on an almost empty propane tank, if you cup the stock pipe opposite the fill valve you can sort of feel the propane flowing in
I haven't had a chance to see how many shells I can run through on a fill