Bill - working off memory on this, but I'll get the books out and verify with notations
Its a good day to do it - I think this morning we have the most snow on the ground of this winter (and its spring

)
I don't remember Dr. Norris' book referencing GBE. I thought that tome was written before they met -
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there are references to all three guns with some history of them in one of GBE's books.
After Dr Norris passed, GBE went to Fairhill to meet with Dr Norris' son. And if memory serves, the three guns were laid out in Dr Norris' study and the younger Norris said to GBE that he was to have his choice, if so = all three were in play - he made a comment on the amount of oil the elder Norris used - GBE left with the two barrel Purdey and Dr Norris' unfinished manuscript for another book.
more later
correction - seems he only had the choice of the one Purdey or the Churchill