Excellent collection of Siam T45 and T66 Headstamps…The “Specials” (Tracer etc) were for the T66(?) Vickers Guns, which the RTA had from the Interwar Period.
The Firearms and Ammunition needs were serviced by the Army’s Arsenal at Bungsoo, outside Bangkok, which was mostly British equipped after WW I ( Siam had sent Observers to the Western front)
although Siam still maintained good relationships with Japan, getting the New (Arisaka based) T66 Rifle, as well as the “New” T66 Cartridge which is a “Product improvement” of the Japanese 8mm Murata Cartridge (case), made in order to “upgrade” the Older 8x50R chambers easily to a Spitzer cartridge ( Simple Ream out of a few Thous of an Inch on body size, and slightly longer chamber to eliminate eroded Throats on the 8x50R chambers). A recalibration ( machining) of the rear sight ramp adjusted the sights to the Flatter shooting T66 Cartridge.
It is unknown if any of the Earlier Mannlicher M88/90s were also converted, but Photos do show them being used as “Trainers” as late as the 1950s.
The “Sako” made 8x52R Ammo was more for the Surplus Market, as by that time, Thailand had changed to .30 cal and Later 7,62/5,56 calibres. The Sako ammo ( Commercial Sako Packets) was on sale in Italy for Siamese Mausers as early as the 1970s, when Thailand had already surplussed its T45/66 Mausers ( I had acquired some Rifles back in 1972-3, in Aussie)