How long will my secondhand Browning B425 last me?
Modern guns like your Browning will withstand the firing of hundreds and thousands of cartridges and last a lifetime as long as you care for it properly and keep it clean.
Neglect is a gun?s biggest enemy, regardless of who made it or how much it cost.
Whenever you clean your gun you should make a special point of wiping the bearing surfaces with a soft cloth to remove any tiny abrasive grit particles, then smear a good quality grease over the knuckles and hinge pin or stub pins before re-assembling the gun.
Do this every time and you will minimise wear and thereby extend the life of the gun.
Finally, take the gun to a practical gunsmith from time to time and let him have a look at it ? he will replace weak springs, worn parts and make any necessary adjustments to ensure it continues to work perfectly.