Why does the bolt on your western field rifle get stuck?

if it is stuck after it has been fired, it is evidence of a dirty or perhaps a corroded or an eroded chamber. The dirty part is easy to cure... clean it. The eroded or corroded chamber should be left to a gunsmith. Usually they can polish the chamber enough to make the sticky problem go away... however it will occur again at some future date. Upon firing, the brass flows into the irregular pits or groves in the chamber making extraction difficult.

If it sticks when it is open, clean it and check for the alignment of the safety or the trigger sear position. If it needs more than cleaning, see a gunsmith.

Keep in mind, Western Field is not exactly the "top of the line" equipment. I am not saying they are bad, however, maybe you should consider trading it off for a better quality firearm.