My answer above, was based on the single photo in the GGCA site. I couldn't get the ones in the link above to "blow up", but based on the comments from Vic and the guy asking about it,it may very well be as raimey surmised, a 6.5mm of some type, from the 4th month of 1910.To determine more would require much better photos and slugging the bore and a chambercast. The scale of the bore in the photo of the muzzle seems larger than 6.5mm.
Mike