His extraction problems are almost impossible to be caused by a long chamber. Why are we steering him this way? A long chamber is a concern in general for a used gun but it does not match his symptom.
If there is a danger it is over pressure from a tight chamber, severe fouling, or something else. Most likely it is just a rough, corroded, or dirty chamber.
To the OP, have you inspected the bore with a light? Can you post pictures of your fired cartridges (detail on case head and primer)?
Mike