Caliber is 9 X 19 mm
Ammunition used was Winchester white box 115 grain FMJ target rounds. Not +P.
Hammer was in the half cocked position so that the safety could be engaged to unload the weapon.
Several people have told you what to do to correct it.
First make sure there are no burrs etc on the mechanism which extracts the shells.
Next wrap some 600 grit polishing cloth around a wood dowel. Constantly turn the dowel in the same direction until you have a high polish on the inside of the chamber, being very careful not to lengthen the chamber at all.
If you have a cratex tip and are careful you can polish the chamber to where the inside is just plain slippery.
Also be careful not to polish to long at any one spot.
The 9mm has a fairly sharp taper so should be pretty resistant to sticking already so I would guess you have a really rough chamber or really hot ammo.