Got this at a gun show last month, real good deal. Then I got the reloading dies off Gunbroker. The brass is obtainable. here is some history.It is a Model 1903 type 45.
The 8x50Rmm Siamese Type 45 cartridge was adopted in the year 1902 for the 1903 Siamese Mauser rifle used by Siam (later known as Thailand). The Siamese Mauser rifle was also known as the Siamese Type 45 Infantry Rifle or the model 45. The model 45 is a modified model 98 Mauser adapted to take a rimmed cartridge. The 8x50Rmm resembles the 8x50 Austrian straight pull caliber. In 1923 the 8x50Rmm cartridge was made more powerful, lengthened and otherwise modified to be more amendable with automatic weapons and was called the 8x52Rmm Siamese Type 66 cartridge. Many of the older rifles were rechambered to the longer 8x52Rmm. The 8x52Rmm cartridge was in production in Thailand until about 1953.
Another difference between the 8x50Rmm and 8x52Rmm was that the older 8x50Rmm used a round nose bullet while the newer offering sported a pointed bullet weighing 181 grains. The 8x50Rmm had a bullet weighing 237 grains and gave approximately 2025 feet per second while the newer 8x52Rmm cartridge gave 2250 feet per second thus increasing the energy and giving a flatter trajectory.
The rifle has the three small rings on the left side of the receiver indicating Japanese manufacture at the Imperial Japanese Army Arsenal at Tokyo (Kowisikawa).
The magazine is completely removable by a small button on the rear of the trigger guard which really well. Like the 98 Mauser the Siamese Mauser has three locking lugs and has a very strong action. Many of them have been modified to such cartridges as the 45-70 and various cartridges based on the 348 case. The action will take any reasonable loads without a whimper. This info was obtained from
http://www.surplusrifle.comMine is in the 8x52 caliber, The rear sight has been modified for this.