A few suggestions -
take some better pictures, especially the serial numbers. It is very hard to see anything in your pics.
Repost (or ask mods to move) to the Commercial and Military Sporting Arms Forum ( http://forums.gunboards.com/forumdisplay.php?f=22
) There are knowledgeable folks there that can help.
A six digit serial number should put it as made in the early to mid-twenties but the stock is typical of a pre-WWI sporter. My first thought was - pre WWI Model C (Army model) but I think the serial # is too high for that. The dated rec'r is also throwing me.
My apologies, I don't know much about the sporters and don't have any books with me.
An original Oberndorf sporter is a great find, hopefully others will be along to help more than I.