We could go on & on for a long time on this without being able to figure out what's going on here. Part of the problem is, you didn't tell us WHY you think the chamber is not for .30-06. Regardless, the best thing for you to do is have a gunsmith perform a "techinical inspection" so that you can know exactly what you have, & whether or not it is safe to fire.

FYI, CMPicon has sold many drill rifles, but they are not always easy to identify. (You can email CMP with the SN & they can tell you if it's a rifle they sold.) Drill rifles were sold by them as "unsafe to fire". Most have weld spots somewhere, but some enterprising folks clean them up & sell them to the unwary as "fresh from the arsenal"; liberal application of grease bolsters that claim.