In Jon Speed book you could find BU-proofed Mauser B Type number 55995 (year 1912), marked as Taucher US Imports, caliber .30-06. So the chamfer casting from yours would be very usefull.
This same book tells that your rifle is Mod B`s pattern No.80 (single trigger, round 24" barrel, tangent curve sight up to 1000 meters).