It's certainly not unusual for a Lindner gun to be underbored. Mine is a 13/1 gun--apparently not messed with much in terms of honing etc, because the bores still measure about .717, which is .012 underbore for a 12ga. Have seen the same thing quite frequently on other older German guns. Of course a 10ga with 12ga bores is way more serious underboring than that.