I have a Holland .500 BPE with a Lyman peep installed in 1903, as indicated on their ledger page. I have seen them installed on several English doubles but my favorite is the peep on the top lever spindle. I saw a Purdey with this type but had assumed it was an older installation. Could this be the one designed by Oscar?? As my eyes are not getting any better, the peep really does help.