Bolt Action Rifles. Wayne Zwoll

can be used in the Siamese action, but not conversely.

      The 8mm Siamese Cartridge

      Generally referred to as the 8x52Rmm Siamese, this is a rimmed, bottlenecked cartridge normally loaded with a 181-grain pointed, jacketed bullet. Not much is known about it—when it was adopted or who developed it. It’s probably merely a ballistically improved version of the older 8x50R Siamese Type 45 cartridge; a little longer case, a pointed bullet and more powder.

      Fred A. Datig in his book Cartridges For Collectors designated this cartridge as the 8x52R Siamese Type 66—so does George C. Nonte in his book Home Guide To Cartridge Conversions. I don’t know what the “Type 66” means. Regardless, if you have the Siamese Mauser rifle and want to shoot it, there is very little chance that you will ever find any factory-loaded ammunition for it. If you are a handloader, Nonte suggests the following: make cases from new 45-70 brass, trim to 2.04” and turn the rim to .560” diameter. Full-length resize in a 33 WFC die, size down the neck and push the shoulder back in an 8mm die until the case will chamber, then fire-form. Use .323” bullets.

      Comments

      The 8mm Siamese Mauser action I received was in very good condition. Very well made and finished, it was as smooth in operation as any military M98 Mauser I’ve ever handled. I have no way of knowing the kind of steel used in making the receiver and bolt, nor do I know what heat treatment was given these parts. If I might guess, I’d say that if the arsenal in Japan that made the Siamese Mauser actions also made Arisaka actions, the same steel and heat treatment were used for both. I know that a file test for hardness is none too reliable, but it can be used to compare the hardness of such parts as rifle bolt heads. To do some comparing I took a file to the locking lugs of a couple of M98 German Mauser bolts, but could not get a good bite. This is normal, for most M98 bolts are very hard. Then I tried the file on the Siamese bolt and I could cut both locking lugs and the front edge of the bolt. Next, I got out two each of the Japanese Type 38 and 99 Arisaka bolts and, with the same filing effort, cut all four of them. Because the M98 Mauser bolt has smaller locking lugs than the Arisaka it is probably a good idea that they are made very hard. I don’t think they have to be made as hard as they are for strength alone so I see no reason why the softer bolt in the Siamese action wouldn’t be just as strong. However, to be on the safe side, the Siamese Mauser action should be limited to cartridges that do not develop much over 45,000 psi breech pressure.

      The 8mm Siamese cartridge (8x52R) has a rim diameter of .561” and is about 2.925 ” overall. You’ll recall that the ad I read called this action suitable for the 45-70, 444 Marlin, et al. I checked a number of cartridges in this action, and here’s what I found.

      45-70. The 45-70 rim is .608” in diameter, too big for the .565” diameter recess in the bolt face. The front of the magazine well (cartridge guide lips) is also slightly too narrow to pass the 45-70 rim. The unaltered magazine will accept and hold 45-70 cartridges, but the bottom or last cartridge is not tipped high enough in front for it to feed correctly. To use 45-70 cartridges, the bolt face recess must be opened up to about .610” and the front of the magazine well widened—not difficult to do. The latter job will most likely end the feed problem of the last cartridge. With these modifications this is a good action for the 45-70 cartridge. Or do as the late George Nonte suggested; turn the rims down to .560 diameter.

      444 Marlin I don’t think the use of this action is going to be too successful with the 444 Marlin cartridge. The 444 rim diameter is only about .514”, and the 8mm Siamese bolt face recess is too large for the too short extractor to hold this cartridge in place for proper ejection. Also, the magazine will not retain the first cartridge inserted into it; similarly, if the magazine is loaded with more than one cartridge, the last cartridge will pop out after the other cartridges have been fed. This last problem can be corrected by rebuilding the follower, but I know of no practicable way to reduce the bolt face recess. Therefore, if you want to use this action for the 444 Marlin I’d suggest you solve the bolt face recess and magazine problem before going to the trouble and expense of fitting a 444 barrel to the action.

      303 British The 303 British cartridge is normally loaded to an overall length of 3.075” and it will just enter the 8mm Siamese magazine, with little length-room to spare. It has a rim diameter of .540”, and it fits the bolt face recess OK, although for better ejection of the fired cases the extractor hook should be a trifle longer. As with the 444 Marlin cartridge, the 303 British case rim is a bit too small for the rear width of the magazine well, and in order for the magazine to retain the first cartridge inserted into the magazine, or the last cartridge after the others have been fed, the right side of the follower ridge (left side of the follower) should be built up slightly. This can be done by sweating (soft soldering) a thin piece of sheet steel onto it. The 303 British cartridge does not fit this action perfectly, but it comes very close, and with the modifications to the extractor hook and follower, the Siamese Mauser action should prove to be ideal for this cartridge.

      Left side of the Siamese action with the breech cover, but minus the tangs.

      Top view of the Siamese action with breech cover closed. Breech cover is independent of the bolt and must be moved manually by grasping the small hook at the right rear of the cover, pulling it out slightly then moving the cover. The spring snap hook locks the cover in either position. The cover can be completely removed by sliding it forward off of the receiver. Below—Action with breech cover open.

      7.62mm Russian This is the old Russian military cartridge with rimmed case, and is not to be confused with the more modern 7.62x39mm Russian or the 7.62mm NATO cartridges. The 7.62mm Russian case has a rim of .564” and is loaded to an overall length of just over 3.00”.just short enough to fit in the magazine of the 8mm Siamese action. The several samples of this cartridge which I have in my collection fit perfectly. Norma has loaded this cartridge for several years and it is a good round for big game hunting. If you want to build a 30 caliber rifle on this action, then the 7.62mm Russian is a good cartridge to choose.

      Other Cartridges

      I found that the 30-40 Krag and the 348 Winchester cartridges are both quite suitable for the Siamese Mauser action. In fact, the 30-40 cartridge with a rim diameter of .545” fits this better than the 303 British. My opinion is that the 30-40 cartridge would be a much better choice than either the 303 British or 7.62mm Russian. Many wildcats have been developed on the 30-40 case—the 6mm Krag, 25 Krag, 35 Krag and the 30-40 Krag Improved. If not loaded to the extreme, any of them would be OK in this action.

      The 348 Winchester is also well suited to this action. Its rim diameter of .610” requires the bolt face recess to be enlarged, but other than that, the 348 functions perfectly in this action. There are also some very fine wildcats based on this case—30/348 Improved, 35/348 Improved, 40/348 Improved, 44/348 and 450 Alaskan.

      Gunsmithing

      Because it is a basic M98 Mauser action, most gunsmithing work that has to be done, or can be done, on a regular M98 for sporting rifle use can also be done on this oddball Siamese Mauser. For example, the bolt handle can be altered as usual by heating the shank and bending it down, or forging it in bolt handle bending blocks, or by cutting off the handle and welding it or a new bolt handle into the new position. Low scope safeties made for the M98 Mauser can also be fitted to this action. Several commercial M98 adjustable single stage trigger mechanisms will also fit, though on some it would be a good idea to heat and bend the finger-piece of the trigger back so it will position better in the trigger guard bow.

      The breech cover can be removed and discarded, its guide rails ground off level with the receiver, and almost any top scope mounts made for the M98 Mauser can be fitted to the receiver. A receiver sight for the M98 Mauser will also fit this action. The breech cover can be retained and used with a receiver sight, but if this is done, the