Husqvarna M40 “Lahti”
Tips for working the Swedish “Iron Stove,” here’s how to maintain and repair the Husqvarna M40 “Lahti” pistol.
I see a sad and disturbing trend locally; a number of aging, older "baby boomer" firearms enthusiast-collectors whom I’ve known for decades are either in decline or have passed away and their collections are being liquidated to meet expenses and settle estates. If it’s happening here, it’s taking place all over.
Consequently, there are a number of somewhat uncommon collectible firearms coming available to "new caretakers." Those who acquire these firearms may require professional gunsmithing services for these new-to-them acquisitions. Examples of such firearms are the L35 and M40 Lahti pistols produced in Finland and Sweden, respectively, shortly before and during World War II.
These heavy handguns were specifically designed to be robust and operate reliably in harsh northern winters, a role which they performed exceptionally well. Not often seen today but somewhat common in the years following the reintroduction of surplus firearms in the mid-1980s, the Lahti is at first glance often mistaken for a German P.08 Luger but the resemblance stops at appearance and grip angle.
Finnish M35 Lahti pistols first saw action in the Russo-Finnish Winter and Continuation Wars of 1939-40, and while most production had ceased by 1950, they were still in active military service well into the 1980s. Note to readers who also sell firearms, the Finnish M35 is much more scarce than its Swedish near-twin and significantly more valuable.
In 1929 Finish officer and arms designer Aimo Lahti developed a robust semiautomatic pistol that could handle severe Scandinavian 08 Luger because designer Aimo Lahti borrowed several features including the grip angle, location of the safety and takedown levers, and the general shape, mounting, and fastening of the grips. But the Lahti is altogether a very different pistol. winters better than the P.08 Lugers then in use by the Finnish Army and Civil Guard.
The resulting firearm was chambered in 9×19 and adopted by Finland in 1935, designated as the L35. Neighboring Sweden was also seeking anew handgun to replace its aging M1907 Browning pistols, chambered in 9x20mm Browning Long. The German Walther 9x19mm HP (later P.38) pistol was chosen by the Swedish military as the M39, but with the outbreak of World War II and Sweden’s neutrality, non-availability of Germanmade guns as well as licensing and domestic production problems with the M39 proved insurmountable.
Seeing the efficient performance of the Finnish Lahti L35 in the Winter and Continuation Wars between Finland and the Soviet Union, Sweden decided to produce a slightly modified version of this outstanding pistol. The Swedes began to produce their Lahti in 1942 as the M40. The Finns made their pistols at Valtion Kivaaritehdas (State Weapons Factory) in Jyvaskyla, Finland. Sweden produced its pistols at Husqvarna Vapenfabriks AB in Husqvarna, on the shore of Lake Vattern in south-central Sweden.
Both pistols are often referred to today generically as "Lahti" after the designer. The first Finnish pistols were virtually hand built, and sporadic production was twice halted
Even though Sweden was neutral during WWII, cost-saving measures like this one were taken with weapons and equipment. The nut threads onto the recoil spring guide rod, and the end of the guide rod is peened over to capture the nut. Disassemble only to replace parts, making certain needed parts are in hand. by conflict with the Russians in 1939-1940 and again in 1944-1946. When production stopped around 1950, only about 12,000 total Finnish L35s had been made.
Another 1,250 were ordered in 1958, but since much of the Finnish tooling The barrel/extension assembly is withdrawn forward off the frame. The slide was then gone, Husqvarna in Sweden produced a hybrid L35/M40 model for the neighboring Finns. In Sweden, Husqvarna produced over 80,000 M40s and 850 civilian versions of the arm between 1942 and 1946.
Because Husqvarna also is shown partially withdrawn from the extension in this view. made iron kitchen ranges and because the M40 was substantial and heavy, the pistol was nicknamed Järn Spis or "iron stove." Most Swedish M40 pistols have "S. S." stamped in the rear of the receiver above the lanyard loop, signifying inspection and approval by Swedish Army ordnance officer Captain Sture Stenmo.
The first Swedish M40 models produced were nearly exact copies of the L35 except for the captive recoil spring, but the Swedish pistol underwent many changes throughout the production period between 1941 and 1946. Early models had a loaded chamber indicator, a rectangular projection in the top of the slide, but most of these early pistols were refurbished and had this feature milled off and the indicator port plugged.
Most of the Swedish M40 pistols had a larger trigger guard for winter gloves, but a few incorporated small trigger guards. Early barrels have a ramped front sight base and a "trumpet bell" rear end. Later barrels have a straight front sight base and a hexagon nut that abutted the front of the extension; those barrels were lengthened by about 20mm.
The nickel steel alloy that Husqvarna wanted to use was scarce and wasn’t available in quantities needed to make the slide, barrel, and extension, so it was only used for the barrels. Because of this lack of tough nickel steel, cracks started to appear in slides and extensions of M40 pistols in service. Husqvarna produced four types of extensions to correct this problem but due to the design changes, steel quality, and the use of unsuitable ammunition, major slide and extension cracking problems continued.
It didn’t help that Sweden issued m/39B steel jacketed ammo intended for use with sub-machine guns that created excessive high pressure
Far All but the earliest pistols had arrow-marked locking blocks. To remove the safety lever, use either a punch inserted in the hole in the thumb piece or a protected tool such as a small screwdriver with a length of heat shrink tubing applied to pry the safety lever up and over that short pin to get it in the position shown. Rotate slightly farther clockwise to line up the key on the shaft with the opening in the frame and withdraw out the left side. which over stressed the M40 pistol.
In a study made by the Swedish Army, service life of the M40 was estimated at 3,000 rounds using them/39B cartridge. Although Sweden remained neutral during WWII, after the war it trained refugees from Norway and Denmark to serve as police in their respective home countries following the German surrender, equipping them with M40s. Sweden also sold about 10,000 M40 pistols directly to Denmark after the war.
Some unmarked M40s were made which were destined for clandestine work with the Swedish military Secret Service. M40 Remove the takedown lever by placing it in the takedown position as shown behind the trigger guard, and tap it out to the left using a brass punch. To remove the spring from the frame, use a small-diameter punch in the indicated hole to drive the spring out. pistols are still popular in Swedish marksmanship events, and many of these guns are still used by the civil Swedish Pistol Association.
L35 and M40 pistols are not often encountered today in the United States, although some M40s were imported, the majority in 1949-1950, the mid-1960s, and again in the late 1980s through the mid-1990s. These available specimens are eagerly sought after by collectors. Good condition arms, particularly when accompanied by their original holsters and accessories, are increasing in value. The classic Lahti is an interesting and innovative piece of history and deserves an honored place in any military handgun collection.
Looking now at the M40 and its design features and operation, the fact that these pistols resemble the P.08 Luger is not by accident, given that the 7.65mm Luger pistol was the L35’s predecessor in Finland. Initial field stripping is almost identical to the Luger, where the barrel/extension assembly is pushed back slightly, and the takedown latch located in the left forefront of the lower receiver is rotated clockwise and down to release the barrel/slide assembly by drawing it forward.
However, the similarity ends there because the Lahti uses a linearly-translating bolt called the slide instead of the P.08’s toggle action. The barrel is screwed into the box-like extension that encloses the slide and most of the action. The slide has grasping grooves on each side at the rear which are used to retract it manually. On top of the slide there is a U-shaped locking yoke that mates into grooves in both the slide and the barrel extension, serving to lock the two together.
An internal swinging hammer strikes the firing pin contained
The straight surface of the accelerator strikes the left side of the slide (bolt) to impart extra momentum to the slide for reliable function in cold conditions. The larger pin is the accelerator stop pin which bears against the forward projection of the wide end of the accelerator. The M40 will still function without the accelerator installed. within the slide. When the gun is fired, the barrel/extension/slide assembly recoils together about The stop pin and retainer pin are clearly shown.
The slide is in contact with the accelerator at the top and there’s about a 1/4" gap between the accelerator and the frame at the bottom. As the barrel/extension travels rearward with the slide locked to the extension, the slide unlocks as the lower end of the accelerator impacts the frame, pushing the upper end against the slide and driving it rearward. 1/4", then the U-shaped locking yoke is cammed upwards by ramps in the frame, unlocking the slide and allowing it to continue to the rear by itself.
A unique feature of the Swedish Lahti pistols is an ingenious semi-circular rocking "accelerator" which gives the slide an additional kick to the rear. This helps cycling the action when ammunition ignition pressure is reduced by extremely cold temperatures. A coiled return spring in the upper part of the slide loads another round from the magazine and returns the slide to battery and the slide forward.
An idea that sounded good at the time, when firing the SMG 9mm ammo these M40s equipped with the accelerator started to experience cracking of slides and receivers. A large number of Swedish M40s had their accelerators removed to help prevent this from occurring. In 1993, Sweden officially retired the M40 and adopted the 9x19mm Glock 17 pistol as the M88. Unfortunately, about 50,000 of the military M40 pistols still in Swedish armed service inventory at that time were destroyed.
Other features include a holdopen device that keeps the slide back on firing the last round. The magazine must be removed or dropped a short distance to allow the slide to go forward after brief manual retraction. A rotating manual safety is used, placed on the upper rear of the left grip panel similar to that employed on the P.08 Luger. A large ejection port on the right side helps to assure positive ejection of the empty cartridge case.
An eight-round magazine is utilized with a very strong internal spring, virtually necessitating the use of a loading tool which was provided in every military holster. The issue flap holsters also contained two extra magazines and a cleaning rod. Disassembly Field disassembly is very simple. Remove the magazine and pull back on the slide to view the chamber and ensure the weapon does not have a cartridge in the chamber. Return the slide to battery.
Push the muzzle against a Remove the hammer pin and hammer before removing the sear pin and sear. The larger circular feature below and slightly to the left is the right end of the safety lever shaft.
Far Also visible are the trigger reset spring pin just below and to the right of the trigger axis pin. The trigger reset spring is partially visible between the rear of the trigger and the frame. Farther down the trigger is the trigger bar pin. The black arrow indicates the cross hole for the firing pin retaining pin; the extractor is the long rectangular feature forward of that hole.
The extractor is held in place at the front by a pin machined into its inner side that rests in a circular recess in the side of the slide. padded hard surface to force the barrel/extension assembly rearward approximately 1/4", and rotate the takedown lever located on the left side above the trigger guard 90 degrees clockwise to point straight down. Release the barrel/extension and withdraw the assembly off the frame to the front.
With the barrel/extension assembly free from the receiver, push up on the U-shaped locking block to unlock the slide, then remove the slide to the rear. The grips can be removed by unscrewing the grip The extractor is easily removed by prying outward and forward at the claw end to lift the pin from its recess, then tap the extractor farther forward to completely remove it.
The vertical face at the right that intersects the ejector slot is the slide’s feature that the accelerator impacts as the barrel/extension travels rearward. screws and pushing the grip plates off the receiver from inside the magazine well. Note that the top of the grip panels are undercut and are retained by the top edges of the magazine well openings on each side of the frame.
The safety lever can be pried away from the receiver and rotated clockwise to align the keyed safety lever shaft for removal from the receiver. The M40 is now field stripped. Further routine disassembly is not recommended due to the fit of the pins, staking of some parts, and a general lack of availability of replacements from the usual gun parts sources. One is reminded of the phrase, "There are no user-serviceable parts inside" and the Lahti is definitely one firearm to which this adage somewhat applies.
The following paragraphs and accompanying photos describing detail disassembly tips will assist the reader should an M40 in their care require general surgery. The recoil spring is surprisingly small compared to those of other contemporary 9mm locked-breech pistols. It is notable because it is captured by around knurled nut that is screwed onto the recoil spring guide rod at the rear end, outside of the frame. The end of the guide rod is peened over inside the recess of the knurled nut.
For this reason the nut should not be removed unless the recoil spring for guide rod requires replacement and a spare guide rod and nut are on hand. The previously-mentioned locking block is stamped with an arrow on the inside of the "U" that points forward when correctly assembled. Critical point: Make absolutely certain that you install the locking block correctly during reassembly. The safety lever is easily removed by inserting a drift punch into the hole in the safety thumb piece. Use the punch as a lever to
The business end of the holdopen (slide stop) is visible to the right at the front of the hammer recess. Take caution to restrain the magazine catch when driving out its retaining pin to prevent its launch. Note than when reinstalling the magazine catch, it helps to use a slave pin to align the magazine catch and its torsion spring for reassembly into the frame. carefully pry the safety away from the frame just enough to clear a short pin that serves as a stop.
Rotate the safety clockwise until the keyed shaft lines up with the hole in the frame for withdrawal. The takedown lever at the front of the trigger guard is removed by tapping it out with a brass punch from the right once the lever is in the takedown position, pointing straight down. The takedown lever’s round wire detent spring is removed by using a small diameter punch through the tiny hole in the front of the trigger guard.
The semi-circular accelerator is located at the front left side of the barrel extension and kept in place by a spring-loaded small diameter pin. To remove the accelerator, press a suitable small-diameter punch or a large paper clip through the hole in the accelerator to push in the spring-loaded pin, then rotate the accelerator up and out of the inside of the extension. The pin and spring are then removed using tweezers and a pick.
To remove the ejector from the left side of the barrel extension, insert a small screwdriver or other tool to lift the rear end of the ejector from the extension so that the ejector’s locking lug clears its recess in the extension, then push the ejector forward to remove it. The good news is that the recoil spring and guide assembly will not need to be disassembled from the frame in order for the hammer to be removed.
With the hammer forward and the hammer spring relaxed, apply slight downward force to the hammer and drive out the hammer pin, which is the larger and more forward of two pins at the top of the grip frame, located diagonally above the safety lever shaft hole. The hammer and its strut can then be lifted upward past the recoil spring and its guide and out of the frame. The hammer spring and plunger can be removed through the magazine well using needlenosed pliers or tweezers.
Next, drive out the sear pin and remove the sear. Move the trigger bar downward to release the sear. Be careful to not lose the coil sear spring that rests in a recess in the pistol’s rear frame. The Lahti is a bit unusual in that the sear is located to the rear of the hammer. In the majority of pistols, the sear is in front of the hammer. The trigger bar spring is removed by using a small screwdriver to lift the spring leg out of the groove in the bottom of the trigger bar.
The spring is removed from the frame by rotating it through the eye into which is it "threaded," much like a key is installed or removed from a key ring. To completely remove the trigger bar if absolutely necessary, support the trigger and drive out the pin holding the front of the trigger bar to the trigger. Withdraw the trigger bar to the rear and out of the right side of the frame. The disconnector can be removed by sliding it downward out of its slot in the right side of the frame.
If necessary, to remove the trigger drive out its axis pin in the top rear of the trigger area of the frame. A second pin in the trigger retains the trigger reset spring. Once again, it is recommended to remove these pins and components only if absolutely necessary. The same applies to the slide hold open lever on the left side of the frame. Its wire spring is usually staked into the frame. Last, drive out the magazine catch pin in the lower rear grip frame.
To reinstall the magazine catch, make use of a short slave pin to retain the magazine catch spring during reassembly in the frame. As with many other of the M40’s parts, remove the magazine catch only if necessary. Despite its size and heft, the M40 has a history of being less robust than its Swedish designers intended, due to the battering of the barrel extension and slide from the sharp impulse of the accelerator when hot 9mm ammo was used.
The Swedes removed accelerators from some of their M40s as a corrective measure to prevent cracking primarily of the extensions and the slide. These cracks were typically seen in the area of the locking block. Sometimes the frame would crack
1 Front Sight 2 Barrel / Extension Assembly 3 Accelerator Stop Pin 4 Accelerator Retainer 5 Accelerator Retainer Spring 6 Accelerator 7 Ejector 8 Locking Block 9 Extractor 10 Slide 11 Right Grip 12 Grip Screw 13 Firing Pin Retainer Pin 14 Firing Pin Spring 15 Firing Pin in the area around the accelerator. These are points to look for when evaluating an M40 for a customer as to shootability.
Customers should be cautioned to use standard commercial US-made 9×19 ammunition and avoid any 9mm+P, NATO 9×19, or any surplus 9mm.
It is recommended that European commercial 9×19 be avoided because in my experience it tends to be a bit 17 Trigger Pin 18 Trigger 19 Trigger Spring Pin 20 Trigger Spring 21 Trigger Bar 22 Trigger Bar Pin 23 Sear Spring 24 Sear 25 Hammer Strut Pin 26 Hammer 27 Hammer Strut 28 Hammer Spring Plunger 29 Hammer Spring 30 Spring Guide Nut 31 Trigger Bar Spring hotter then US commercial 9mm, as evidenced by being flatter shooting and printing lower on a target at a given distance.
I would refrain from using Sellier & Bellot, Fiocchi, Hungarian, and Turkish brands.
No mistake, that is all quality ammunition, but American commercial 9mm is a bit more docile and more suited to being consumed in the M40 "Iron Stove." AG Husqvarna M40 "Lahti" Pistol (Speci ications subject to change without notice) 33 Magazine 34 Magazine Catch 35 Magazine Catch Spring 36 Magazine Catch Pin 37 Left Grip 38 Grip Screw 39 Safety Catch 40 Sear Pin 41 Hammer Pin 42 Takedown Catch 43 Takedown Catch Spring 44 Recoil Spring 45 Recoil Spring Guide 46 Hold Open Catch 47 Hold Open Catch Spring American Gunsmith Reader Services 1.
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