airmec wrote:
Hi and welcome on the forum chilly732,
I have two Crosman/Benjamin rifles doing the same exact thing. They started doing that after I swapped out the original seal for a (harder) teflon seal. I'm guessing when you dry-fired your rifle it crushed and hardened the piston seal a little, making the piston slam harder than before when fired. If your gun is a non-PAL one and shooting well, I wouldn't worry too much and just follow Lauchlin's advice. If your gun's full power, I'd take it apart for an inspection and main seal replacement.
But before opening the rifle, there's another test you should do: check the breech seal (at the entry of the barrel), if it leaks it can also make the piston slam and ring. There's a simple test you can do to make sure it seals: cock and load the rifle with a pellet, place a small piece of a tissue or toilet paper (1'' x 1'') over the barrel/tube junction (red arrow in first picture), and fire the rifle in a safe direction. If the piece of tissue is blown up when you shoot, there's a leak. Repeat the test by turning the rifle over and place a piece of tissue over the junction underneath the gun (red circle in second pic). If there's no leak on the breech seal, then the issue is the main seal.
HTH and please let us know how it turns out.
I agree this is also a possibility