JBG,

I haven't actually seen this rifle yet since it is in England but hopefully I will receive some pictures soon that will shed more light onto the subject. I was told over the phone that the 500 marked on the lumps referred to the bullet weight that the gun was regulated for. What you said, however, makes more sense based on what I have learned so far regarding the history of this cartridge. Thank you for your help.

Best regards,

Jim