How old is your Canadian sportsman model 269 series E 12 gauge 3 chamber?
I got mine in 1979 so that makes it 32 years old
Where can you find a shell puller for a Savage model 30 series E it is a pump12 gauge with a 3 inch chamber?
Reverse airflow feels a chamber inside the gauge and reads the pressure equal to the inside of the tyre its that simple. Same for air compressure, when the pressure is applied it seals the valve on the gauge end then back pressure fills the chamber inside the gauge when you release the gauge from the tyre valve the pressure has gone!!