Beeman 2004 (P17) .177 pistol

[glam69]

Please could anyone offer any advice on why my Beeman 2004 keeps getting jammed? The pistol cocks ok ie the pressure does build up when pumped and I cannot hear any escaping air, but when the trigger is pulled the pistol goes through the motions of firing, but the pellet doesn’t move and has to be removed with a rod.

How critical is the breech seal as that seems a little worn, also can the barrel move to widen the interference fit between the barrel end and the breech seal?

Additionally does anyone know the seal sizes?

Thanks for taking time to read and thank you if you can help.