No such model. Can't be answered without a detailed description of all markings, finish, barrel length, condition, accessories, box, type of action, papers, etc..
Browning never made a Model 51 shotgun.
Can't answer about "Volunteer" question. Please tell which model. Volunteer is not a model by Browning
Never heard of a model 22 BPS. A Browning BPS in 20 gauge can vary from 150-400 depending on condition.
Browning did not make the Model 11, Remington did. If you have a Remington Model 11 in 16ga, value is between $150-$450.
50-500 USD or so
Impossible to value without a detailed description of all features.
100-1000 usd
Impossible to answer without knowing which model.
Impossible to answer without knowing model.
Requires a professional appraisal
50-650 usd
10-1000 USD or more depending on specifics