I'm about as certain as I can be that it has 12-groove rifling. Twelve grroves can be made to correspond to the numbers on a clock's face. On that sabot, count the groove at 3:15 and you'll see another groove at exactly 4:15, exactly 5:15, and so on, up to exactly 9:15 and then the sabot is broken off. The exact correspondence of the grooves to clock-number position means it must be 12-groove rifling.
Id anybody can't follow what I described above... here's another way. Draw a straight line from the 3:15 groove across the central bolt to the other side of the sabot. You'll see the straight line hits the 9:15 groove. There are five grooves showing around the bottom of the sabot/clockface in between 3:15 and 9:15. That would mean there are five more past 9:15 going around the top of the clock to the one we already counted at 3:15... giving us a total of 12.
Regards,
Pete