You will have to contact Browning to find out.
1971
The BL22 was made from 1970-2003.I would contact Browning directly and their customer service dept can identify the year of manufacture for you.
50-400 usd
The serial number is not correct for a BL22. It should have letters associated within the number. Please re-check and ask again. Thank you
Can't be answered since no serial number was provided.
1971, up to 500 USD
Yes
Try the blue book of firearms value or call browning
Your Browning BL-22 Grade II will bring between 425-450 dollars in the condition that you describe.
I've got a Medalist with an unconventional serial number ( "U" is in the sixth position). This one does have the dry fire mechanism.
You may be able to find an instruction manual on eBay or Auctionarms.com