If it is a break action/single pump the check the O ring at the breach. They are cheap and easily replaced. Take the O ring to the hardware store and find the correct size. It is a lot cheaper than ordering them. Also, have you cleaned the barrel? You could be leaded up.
Patron Member NRA
"I would not be an old man if I had not been an armed young man." JTJ
I was taught to respect my elders but they are getting harder to find.