Here's what my friend had to say:
"Von Lengerke & Detmold was a high end sporting goods importer and retailer in New York with a sister outlet in Chicago named Von Lengerke & Antoine. They both sold out to Abercrombie & Fitch about 1930. The firearm he wants to know about is probably a middle grade British "midlands" Birmingham mfg. The proof-marks on the water table and barrel flats would tell a lot.
So, what are the proofs?