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Mauser Miscellany FdH

The Model 98 Mauser 22 rimfire conversion unit installed in a WWI M98a carbine.

Erma 22 Rimfire

Conversion Unit

LUGER FANS HAVE long been familiar with the Erma 22 rimfire conversion unit made for that pistol. Not so well known, however, is the 22 Long Rifle conversion unit this firm (Erma Werke in Germany) made for the M98 rifle. I believe this unit was made in the 1920s and ’30s, but I don’t think it has been made since before WWII. The conversion unit illustrated here is unmarked (except for serial numbers and proof marks), but I believe, and several other Mauser fans agree with me, that this is the Erma unit.

This, or a similar conversion unit, was also used by the military in Geramny for training purposes. It was called the “Model 24 Insert Barrel.” It was most likely first made as a single shot, then as a repeater later on. These were probably by Erma.

This conversion unit has the basic mechanical components of a rifle—a complete action and barrel assembly but minus sights, trigger and stock. The action is a turnbolt, the cartridges fed into it from a detachable box magazine. Only the bolt and floorplate/follower assemblies must be removed from the M98 rifle for the unit to be installed. It was made primarily to be used in any 8mm M98 military rifle or carbine having a barrel at least 24” long, but it can also be used in 8mm Mauser sporting rifles with similar length barrels.

The receiver of this unit fits in the receiver of the M98 in place of the regular bolt. The main length of the barrel is only slightly smaller than the land diameter of the 8mm barrel, so it fits snugly in the bore. The breech end of the barrel is the size and shape of the chamber. On the breech end there is a collar and, between this collar and the receiver, there is a two-piece threaded adjustable sleeve arrangement. One part of this sleeve has two lugs which can be rotated to engage in the locking lug recess in the M98 receiver. When the unit is inserted into the M98, the outer sleeve with its lugs is turned clockwise to engage the lugs in the receiver, then the inner sleeve is turned clockwise to secure the unit in the rifle. Holes are provided in both outer and inner sleeves so that they can be turned with a tool, such as a nail with its point filed off.

The front part of the unit’s receiver has two openings; one at the bottom for the magazine, one on the top right for the ejection port. The rear part of the receiver, larger than the main part, is made to fit in the larger opening in the M98 receiver and over the top of the tang. This prevents the entire unit from turning in the receiver. The barrel is attached to the receiver with two cross pins.

The bolt has three main parts; the two-diameter bolt body, which contains the long extractor and separate firing pin; the bolt handle sleeve, which threads into the rear end of the bolt body, and the firing mechanism composed of striker, mainspring, cocking piece, safety and striker nut. A slot is milled in the thick rear part of the receiver for the bolt handle, and a notch cut in this slot for the base of the bolt handle to lock the bolt in the receiver when the bolt is closed. The bolt stop is merely a shoulder in the rear zig-zag slot for the bolt handle.

The cocking piece has a projection which extends through a narrow slot in the bottom of the receiver and into the cocking cam raceway in the M98 receiver to engage the sear. The striker is cocked entirely on the closing motion of the bolt. When the action is cocked, the wing safety can be rotated down to engage over the end of the receiver.

The detachable five-shot box magazine is well made. The milled follower is guided inside the magazine by its rounded front end moving in a cylindrical guideway built into the front of the magazine. The coil magazine spring is positioned in this cylinder. The magazine is precisely and securely held in position through a hole in the floorplate, inside of which is attached a sheet metal guide housing. A notched flat spring attached to the right side of the magazine holds the magazine up when the notch engages over the edge of the floorplate. The bottom of the magazine and its release spring project below the magazine floorplate so that it can be easily grasped and removed.

The unit illustrated here is very well made, fitted and finished, and all the major parts are numbered.

To install the unit in an M98 rifle, remove the bolt assembly, floorplate, follower and follower spring. Turn the locking sleeve on the Erma unit so the hole in the rear part of this sleeve is up, then insert the unit into the receiver and barrel as far as it will go. Pull the trigger or open the bolt of the unit so it will stay forward. Now rotate the locking sleeve ¼-turn clockwise until the locking sleeve can be turned. When the locking sleeve is engaged, turn the adjustment sleeve clockwise until tight. Install the floorplate, slip in the magazine and the rifle is ready to fire.

I fired the conversion unit shown here at an indoor 50-foot range, using standard velocity 22 Long Rifle ammunition. Taking a fine bead over the crude military sights on the M98a carbine in which this unit was fitted, and with the rear sight elevated to the 600 meter setting, the shots zeroed perfectly in the target. Considering the crude sights, accuracy was quite good, suitable for plinking and small game at close range. The unit functioned perfectly and there were no feeding, ignition or extraction problems.

Close-up of the conversion unit, shown with bolt open.

The complete 22 conversion unit for the M98 rifle in 8mm (8x57 or 7.9x57) caliber. Unit is shown with bolt open. The Erma units were usually supplied in a partitioned wood box with an extra magazine and instruction sheet.

These Erma conversion units are seldom seen today, but they’re an interesting extra for any Mauser rifle collection.

Mauser M98 Breech Cover

One of the rarest accessories ever made for the M98 military rifle was a breech cover. During the early part WWI, the Germans discovered that their M98 was not as foolproof as it could have been. The main fault showed up when the rifle was used in all sorts of battle and weather conditions— in mud-filled trenches, on dusty, sand-swept battle grounds, or in freezing rain. Then it could become inoperative, or its operation affected, by the entry of foreign material into the action.

Among the several openings in the M98 where foreign material could easily enter, the largest is the thumb notch in the receiver wall, which exposes the left locking lug raceway. This opening is large enough, front and rear, to allow foreign matter to enter the locking lug recess in the front of the receiver and even go inside the bolt, through the two large gas escape holes, and rearward into the bolt-stop and ejector openings. Other openings, especially during rain and freezing weather, are the clip guide slot in the bridge, the space between the bolt sleeve and bridge which exposes both ends of the bolt guide groove, and the space between the extractor and bolt. The problem was evidently considered serious enough to warrant development and manufacture of a breech cover to shield these openings.

Unlike the Type 38 and 99 Arisaka military rifles, whose actions were initially designed for a sliding cover, the M98 action was not so designed, and a cover had to be made to fit it. This was accomplished, as shown in the illustrations. The cover was so constructed that it could be easily attached to the unaltered Gew-98 rifle with the straight bolt handle. Although it was a sort of make-shift affair, the cover did effectively shroud the greater part of the action.

This breech cover consists of two main parts: the cover and the clip by which the assembly is attached to the rifle. These two parts are attached to each other by a telescoping hinge joint, so the cover will open and close with the bolt.

The clip is made from a piece of wide spring-tempered steel. The top of this clip encircles the exposed top part of the breech end of the barrel, between the rear sight and barrel shoulder, then extends over the left and underside of the forend. It is made with enough spring tension so it is not easily unsnapped from the rifle, once it has been pressed into place.

The cover, which is also made of spring-tempered sheet steel, is accurately formed to enclose most of the top of the action. It extends from the rear of the receiver ring to just forward of the safety, and is wide enough to cover the top of the receiver ring and run over the edge of the stock. It’s wider at the rear to cover the entire bolt stop, bridge, the flared part of the bolt sleeve and the root of the bolt handle. The rear end of the cover is turned inward and cut out to conform to and contact the contoured surface of the bolt sleeve. The rear right side of the cover is notched to fit over the bolt handle, and a simple spring bar latch, fastened at the edge of the cover over the notch, loosely fastens the cover to the bolt handle.

The critical part of the breech cover assembly is the telescopic hinge on the left side. The outer part of this hinge is a steel tube securely fastened to the left of the clip. This tube extends about halfway back on the cover. A long thin spring rod, rolled into the rear left bottom edge of the cover, extends forward into the tube to complete the telescopic hinge, allowing the cover to open and close and slide backward and forward as the bolt is operated.

When the breech cover is in place, and the action closed, it effectively encloses the main part of the action, protecting it against the entrance of foreign material. The cover in no way interferes with the normal operation of the safety, and when the action is open it does not obstruct loading the magazine in any way. On opening the action, however, the cover rises on the bolt handle stem and this makes it necessary for the shooter to grasp only the ball of the bolt when the action is operated.

The breech cover is readily removed by first releasing the bar latch under the bolt handle stem, swinging open the cover and drawing it to the rear to separate it from the clip. The clip can then be removed by pressing the underside of the clip to the left, until it separates from the forend.

Apparently the breech covers were not widely used since they are scarce today. Perhaps they were not developed and made early enough to be used before WWI ended, or maybe the cover wasn’t entirely successful.

M98 breech cover in place on the rifle, showing the bolt handle and breech cover raised with action open.