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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 finish on my weapon is good for a military rifle and the action is pretty smooth while the trigger is the typical two-stage military trigger. The stock has some of the usual dings that come with a rifle of this age but I think that gives the rifle character. Many of the rifles were made in Japan as well as in Thailand at their arsenal in Bangkok. My 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. In fact I had one in 45-70 that I loaded with a 400 grain bullet up to 2300 feet per second without any problems. In fact your shoulder may give out before the action. The action is capable of accepting many other larger rimmed cases as long as they aren’t real long because of the magazine length. The 7.62x54 and the 30-40 Krag are good choices for rebarreling. Personally I would not alter one unless the barrel was shot out and the rifle was otherwise in bad shape excluding the action. 

For brass I found that the 45-70 cases is the best one to use. The rim has to be cut down and the case sized correctly in order to obtain good cases. Case length is 2.04” while the rim is .560” in diameter. If you are making your cases I suggest an intermediate step by partially necking down in a 33 Winchester die. Then size it until the case chambers in your gun. A company www.buffaloarms.com can make those and other cases for you and their work is always top drawer.  I have developed and chronographed some loads that are safe in my gun but you may want to approach from below with the full power loads.

Loading it is straight forward as in most military cases. I use 323 diameter bullets except the cast are 324. To save money on dies I found that the 8 mm Lebel dies work fine and the 8mm Nambu belling die was used to bell the cases for cast bullets. Like most rifles cast bullets can be used to good effect on targets or small game. I have found that at close and moderate ranges cast bullets kill small game cleanly without destroying much meat. In many instances they produce accuracy equal to jacketed bullets. I didn’t try and extract the last foot second out of the loads which seldom is necessary. The cartridge is adequate for hunting most big game. I used seven shots for my chronographing with the near screen being ten feet from the muzzle. The e.s. mentioned in the comments is the difference between the fastest and slowest shot. Anything under one hundred feet per second is considered good while under fifty is fantastic. That indicates very consistent ammo for that rifle. I feel confident that I could increase the top loads a bit with that 98 type action however I don’t see the need.  Accuracy is adequate for most applications in view of the sights. Young eyes and good light can produce pretty respectable accuracy with the best loads. A clamp on type of scope mount would without a doubt add to the accuracy and useful range of this fine weapon.  Another thing to remember is there are many 8 mm calibers out there. Some have similar designations but are not interchangeable. There are at least 3 - 8X50 chambered rifles: the 8x 50 Austrian straight pull , the 8mm Lebel and the 8x50 Siamese.  These cartridges are not interchangeable and it IS dangerous to fire the incorrect round in the wrong rifle. If you are not sure what your rifle is chambered for then have a gunsmith look over your weapon.

I doubt that you would find much surplus military ammo for this rifle and if you did it might not fire, especially the older 8x50Rmm. Another downside to firing this surplus ammo is that it in all probability it has corrosive primers. If you shoot corrosive ammo in your rifle you will need to clean the rifle to avoid rust and pitting.    

Like most of my other weapons this 8mm is very dated, but I prefer these types of guns to the newer assault and military weapons. Like the old cars they just have more character then the newer weapons.

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