Bolt Action Rifles. Wayne Zwoll

wooden handguard held in front by the middle barrel band with the front sling swivel attached thereto. The rear sling swivel is screwed to the bottom center of the buttstock. The front and rear sights are typically M98 Mauser, with the graduation markings in unusual Siamese numerals. If the rifle is complete, its most identifiable feature would be the sliding breech cover which is not connected to the bolt and must be moved manually. Another distinctive feature is the Japanese Arisaka-type tangs to strengthen the grip area of the stock. Siamese

      Action Markings

      The 8mm Siamese action I have shows several distinct markings. The Siamese crest, or coat of arms, is stamped on the top forward part of the receiver bridge. This crest is round and about

” in diameter. A line of five Siamese numerals or letters is stamped on the receiver bridge below the crest, and another line stamped across the bridge. Although I have been unable to get these lines deciphered or translated, they probably refer to the date of manufacture and model designation. The Japanese arsenal proof mark, three interlocking circles, is stamped on the left receiver wall. Arabic numbers are stamped on various parts of the action, but those which are apparently the serial numbers are stamped on the flat bottom of the receiver ring and on the left side of the front tang of the trigger guard.

      The Action

      The 8mm Siamese is a copy of Paul Mauser’s M98 turnbolt action with certain modifications and additional features that make it one of the most distinctive and unusual forms of the basic M98. The modifications are essentially those needed to handle the 8x52R Siamese cartridge; the additions which are of Japanese influence include the detachable tangs and the sliding breech cover.

      By carefully comparing the 8mm Siamese specifications with those of other M98 Mauser actions covered in this book, and by studying the photographs of this action and the others, it is easily seen that this is a peculiar variation of the Model 98 Mauser.

      First, let’s see what this 8mm Siamese action has in common with the regular M98 military action made for the 8mm Mauser cartridge. The receiver is of the same general pattern and configuration, it is the large ring type and has the regular collar inside the ring, slotted only on the right for the extractor. It has the clip-charger guide slot in the bridge and the deep thumb cut in the left receiver wall. The receiver will accept a standard-length M98 bolt, though the receiver is only 8.50”, or .250” shorter than the standard M98. The receiver is flat on the bottom and has the integral recoil lug like all other M98 actions.

      Siamese Mauser action open, tangs in place and breech cover slid forward.

      Except for the bolt face and cartridge head recess, the bolt and firing mechanism are an exact copy of the M98 bolt. The straight bolt handle has a pear-shaped grasping ball. The bolt has dual-opposed forward locking lugs with the left (top) lug slotted for the ejector, a third rear safety lug, a guide rib, and twin gas-vent holes. The extractor is the same except that the hook is a bit narrower. The bolt sleeve, bolt sleeve lock, safety, firing pin, mainspring and firing pin head are enough like the standard M98 parts that they are almost, but not quite, interchangeable.

      The bolt-stop and ejector are of the standard M98 pattern except that the ejector spring is riveted to the bolt-stop spring. The sear is also standard, but the trigger stem is cocked back a bit to bring the fingerpiece to a more rearward position.

      In addition to these similarities, the Siamese action has the same functional features as the standard M98, including cock-on-opening, safety operation, extractor camming, etc. Also, everything is disassembled and reassembled in the same way.

      The differences between the two actions are:

      1. The breech cover. The Siamese action is fitted with a very neat spring-steel breech cover which slides to the rear to cover the loading and ejection port, and forward to expose the port. On each side of the receiver there is a narrow raised integral guide-rail over which the sides of the cover engage and slide. This is unlike the Japanese Arisaka receivers which are grooved for a sliding cover. On the right side of the Siamese Mauser breech cover there is riveted a hooked catch which engages notches in the side of the receiver ring and bridge to hold the cover either open or closed, and by which the cover can be slid back and forth. It is entirely independent of the bolt; it must be moved manually by grasping the hooked catch and pulling it outward. The cover can be removed by sliding it forward off of the receiver. The bolt can be operated and the rifle fired with the cover in any position, but it must be open to eject a fired case or to load the magazine.

      2. Receiver shroud. The front end of the receiver has a shroud or collar extending about

” forward as on the Polish Radom M98 Mauser. The purpose of this collar is to hold the rear of the handguard in place.

      3. Barrel shank threads. The receiver is threaded to receive a barrel shank about .990 ” in diameter with 14 V threads per inch. The regular M98 actions have a pitch of twelve threads per inch and usually for a thread diameter of 1.10”. The Siamese barrel is made with a shoulder large enough to abut and “set-up” against the front face of the receiver rather than having the breech face of the barrel butt against the inside receiver collar, as in the regular M98 action.

      4. Left receiver wall. The 8mm Siamese receiver ring is slightly larger in diameter than the large ring M98 action, but unlike the latter, there is no “step” between the left side wall and the receiver ring. This means that the left receiver wall is much thicker in the Siamese receiver, and the reason that it is so made is because of the breech cover guide rails. The average M98 Mauser left side wall is about .155” thick, while the Siamese Mauser is about .200” thick.

      5. Bolt face. The recessed bolt head will accept a cartridge rim no larger than about .564”. There are no lips extending forward on the left side of the rim recess as in the regular M98 Mauser action. The rim recess is cut away at the bottom to allow the cartridge rim to slip under the extractor hook on feeding a cartridge from the chamber, which prevents double loading.

      6. Extractor hook. It is narrower than the extractor, being only about .300” wide.

      7. Tangs. Separate upper and lower tang extensions on the 8mm Siamese action extend rearward about 3” and are inletted into the top and bottom of the grip of the stock. They are milled at the front end to fit closely against the rounded end of the integral receiver tang and trigger guard, and are held in place by the rear guard screw. The tangs, connected at the rear by a screw, are almost exactly the same as those used on the Type 38 Japanese Arisaka 6.5mm rifles and carbines. They are used to strengthen the grip area of the stock.

      8. Magazine. The combined trigger guard/magazine is of one-piece milled steel construction like the regular M98 Mauser. The front and rear ends of the magazine box, however, are slanted forward at a sharp angle. This slanted magazine box permits easy loading of the larger rimmed 8mm Siamese cartridge, the slope preventing their rims from catching on each other. Each cartridge pushed into the magazine moves to the rear so that the next cartridge inserted over it will have its rim ahead of the cartridge rim below. To gain adequate magazine capacity, the rear of the magazine box was made about ¼” deeper than the regular M98 8mm Mauser. The floorplate of the Siamese action is not hinged, but is quickly detachable via a latch built into the forward part of the trigger guard bow. Due to the slanted magazine box, the trigger guard bow is positioned back farther than the regular M98 and for this reason the trigger shank is bent back as mentioned earlier.

      Bolt head of the Siamese action, showing: (A) twin gas-vent holes; (B) extractor; (C) right (bottom) locking lug; (D) undercut cartridge head recess; (E) ejector slot, and (F) slotted left (top) locking lug. The bolt also has the regular M98 Mauser short guide rib and the rear safety locking lug (not shown).

      Incidentally, the front and rear guard screws of the Siamese action have the same thread pitch as the regular M98 Mauser guard screws, but the Siamese screws are slightly