Mosin M91 | Great War Armoury

One Rifle for Centuries

3-линейная винтовка Мосина обр. 1891г.

Commonly known as the Mosin-Nagant in the West, Mosin's rifle was Russia's step into the age of modern firearms. Despite a myriad of flaws, the Russian Empire and its successor states would keep it in service with only minimal changes right up to the 21st century.

History

Despite an only beginning phase of industrialisation, the Russian Empire, shortly before the start of the revolutionary time in small arms development the 1880s would prove to be, was arguably equipping its troops with one of the best rifles of the time - the Berdan II, developed by US inventor Hiram Berdan.

The Russo-Turkish War however (1877-1878), and here the Siege of Pleven in modern day Bulgaria in particular, showed the need for new development. While Ottoman sources traced the obscene casualties suffered by the Russian coalition troops back to outdated tactics, European observers of the time took note of the Ottoman use of single-shot rifles to engage at long distance, while repeaters (Winchester Model 1866 in this case) were used to repel attacks closing in on their positions, kickstarting the adoption of repeating rifles across the continent.

Initial trials focused on adapting the existing Berdan II rifles to become repeaters through the addition of a magazine system.
Wisely however, the Russian commission split the task of updating its forces into two main components:

Adopting a new magazine system for use on the existing rifles
Adopting a new rifle entirely

This allowed for inventors to focus on either one of those tasks, or both simultaneously.

Sergei Ivanovich Mosin (1849-1902)

While few meaningful changes were made, over the course of its development there have been quite a few variations in the M91 pattern - some more peculiar than others, like an intermediate version that only bore a sling swivel on the magazine (note that this example received Austrian style swivels in addition on the fore- and buttstock)

Various designs were brought in and tested over the following years, however in 1889 the Russian Ministry of War managed to acquire a sample Lebel Mle. 1886 from France. While Poudre B was still a state secret, the rifle alone cut down on a lot of development time for the Russian commission as barrel and sights were by and large copied from the Lebel, allowing for the inventors still in the race to focus on the action itself, as well as an accompanying magazine system.

The same year, three rifles were submitted - two in a three line calibre, one in 3.5 line*.

With trials being concluded in 1891, two of the rifles were left standing. The 3.5 line design presented by Belgian inventor Léon Nagant, and a native design by Сергей Иванович Мосин (Sergei Ivanovich Mosin) with a smaller three-line bore.
Ultimately, the simpler design and disassembly procedure introduced by Mosin won over the more refined, but complicated one by Nagant, who still won a sizeable sum for the use of his patented magazine, which the Russians had to pay for due to their initial production being contracted in France, where Nagant had patented his design.
While his magazine (albeit modified by Mosin as well) gave rise to the double name Mosin-Nagant in the West, the rifle was officially adopted as the 3-линейная винтовка Мосина образца 1891 года (3-Line Rifle, Mosin, Model of 1891).

Production thus began in 1892 at the three Russian arsenals Тула, Иже́вск and Сестрорецк (Tula, Izhevsk and Sestroetsk), with an addition 500,000 being ordered from Châtellerault in France.

Although changes were minimal by comparison to other rifle lineages, the Mosin went through a few limited changes before its first real trial by fire in the Russo-Japanese War of 1904-1905.

These changes included:

Getting rid of the finger spur early rifles had until 1893
Addition of an upper handguard and subsequent changes to the barrel bands
Changes to cleaning rod length and attachment within the stock

After the devastating defeat against the Empire of Japan in September of 1905, the rifle underwent the most influential modifications starting in 1908.

The adoption of a conical bullet required a modification to the sights copied from the Lebel. In order to simplify this process as much as possible, the sight graduations on the base were kept, and a new, curved ladder installed, at the expense of ruggedness. The new projectile also allowed for the ladder to go from 2,700 аршины to 3,200 аршины (Arshins)**. The higher pressure generated by the new cartridge additionally required a recoil lug to be set in the stock.

As war broke out in the midst of the update process, Mosins can be found with any of the aforementioned features.

One peculiarity that is special to the Mosin is the fact that the rifles were sighted in with bayonets attached.

Unlike contemporary powers that moved away from side-mounted spike or Yataghan-style bayonets in favour of underside mounted knife or spike bayonets, the Russian Empire stuck with a side-mounted spike bayonet that was to be attached at all times via a screw-locked collar behind the front sight. While cutting out the time needed to fix the bayonets in case of need, it caused the rifle to become even more front-heavy.

Serbian troops in particular were very displeased with this fact as they did not keep the bayonets attached on the rifles they received as aid during the war, causing a notable shift in point of impact.

Mosin's rifle would outlast the Russian Empire in spite of all of its shortcomings. With millions produced for its own army, hundreds of thousands sent abroad as aid and even more captured by its adversaries, to be used against its home country.
Mosin's legacy would go on even long after the fall of the monarchy and become one of the most produced firearm systems in history. Approximately 37 million were produced by the Russian Empire and its successor, the Soviet Union alone, ultimately serving in both world wars with almost negligible changes to its overall setup.

The nation that would attempt to get the most out of the platform turnt out to be Finland. With hundreds of thousands of rifles in storage after declaring independence from the Russian Empire in 1917, the Finnish, over the following two decades, would improve the system as much as possible, improving bolts, magazines, sights and stock setups. Finnish troops would go on to wield their own Mosin variants with great success in the Winter- and Continuation Wars of 1940-1944.

Like the cartridge developed for it, the famous 7.62x54mmR, which as of today is the oldest serving cartridge in military use on Earth, the Mosin is seeing use today as well in various conflicts and even on its home turf in the hands of Russian troops and Pro-Russian separatists in the ongoing Russo-Ukrainian War.

A severe lack of small arms had the Russian government scramble to get almost anything that would fire a bullet into the hands of the soldiers. Japanese Arisakas, Italian Vetterli-Vitali, French Berthier or American made Winchester lever action rifles - with the minister of war calling rifles "more precious than gold" it mattered little so long as it arrived at the front

Russian troops on parade carrying M91 rifles

Mechanism

Bolt

The M91 features a rotating bolt with two front locking lugs that, untypically, lock horizontally into the receiver. The bolt head is separate and recesses into the body, with a spring-loaded extractor snapping over the cartridge rim only as the bolt closes, making it a push-feed mechanism like the French Lebel.
The bolt handle is attached to a guide protrusion, operating within a split rear receiver bridge.

On the downside of the bolt another guide rib or bar can be found that double acts as a disassembly tool. Its core functionality is the prevention of the bolt rotating while out of battery and stabilising the bolt travel.
The safety is the simplest part of the entire Mosin bolt. The cocking piece, whose rear end also acts as a gas shield as the Mosin lacks any other gas mitigating features, can simply be pulled back, turnt left and rested onto a milled out section of the left receiver wall.
Additionally, bolt removal is achieved simply by pulling the bolt fully rearward and pressing the trigger.

Magazine

The M91's magazine, Nagant's contribution to the rifle, features a protruding single stack magazine fixed to the action.

Loading happens through proprietary chargers for five rounds each. The charger guides are milled into the split receiver bridge at the back of the receiver.

Internally the magazine is very simple, with two arms raising the follower, supported by a spring. Despite the core being a Nagant design, Mosin influenced the part in so far that Nagant's initial design did not have a dedicated follower.
Additionally the ability to easily remove the magazine floor together with the follower assembly is a solution Mosin came up with.

As the M91 is a push feed rifle, there is an inherent chance of double-feeding happening, meaning a cartridge being chambered partially without being fired and a second cartridge being fed into its back, the bullet tip potentially setting off the primer of the previous cartridge, leading to detonation out of battery.
In order to prevent this, the M91 utilises an “interrupter” mechanism within the receiver, a small part that prevents extra rounds from slipping into the path of the bolt before it has been fully closed on the previous cartridge and thus allowed for extraction of it.

Bayonet

Despite being state-of-the-art in a variety of fields, the Russians stuck with an almost archaic way of attaching the bayonet.
Unlike contemporary rifles, who utilised a variety of lug designs to lock onto corresponding slots on their bayonets' pommels and being held there, the M91 bayonet is a socket type with a screw-locked ring.
This means that the bayonet can not be disattached without tools, as it was intended, with the rifles being sighted with the bayonet attached.

The later M91/30 model in use with the Soviet Red Army would rectify this partially by adding a push button release for the locking collar.

Markings

Manufacturer, Barrel Date, Ownership Mark & Serial Number

The big eye catcher when it comes to Mosins. Sitting atop the barrel shank, you can find the manufacturing arsenal, the year of manufacture (of the barrel, the receiver data is hidden underneath the stock on the tang) as well as the serial number.
Above and beneath it on the receiver you can find the Imperial eagle, acting as both an ownership and an acceptance mark. Other nations that would receive these rifles as aid would oftentimes deface them.

Before the war you can find four different manufacturers:
Oружейный завод Шательро (Manufacture d'armes de Châtellerault)
Тульский оружейный завод (Tula Arms Plant)
Сестрорецкий оружейный завод (Sestroretsk Arms Plant)
Ижевский оружейный завод (Izhevsk Arms Plant)

Proof, Accuracy & Inspection Marks

Inspection marks appear across many components. These include small crowned eagles, Cyrillic inspector initials (Latin in case of the French or later US contract rifles), or cyphers, found on the receiver, barrel, bolt, and smaller parts. They attest to acceptance at different production steps.
Each arsenal had its own set and symbols, with Tula using a hammer, for example.

The proof mark presents as a П ("P") on the barrel shank. Additionally a mark indicating passing of an accuracy test can be found in shape of a K, also on the barrel shank aside the imperial eagle.

Stock Roundel

On the buttstock the manufacturing arsenal would put a custom roundel with its name as well as the manufacturing year of the rifle. Note that these are often faded.

Contract & Capture Rifles

Most capture marked Mosin rifles you will find today bear Finnish markings or modifications as well. After the war, the newly independent Republic of Finland bought large quantities of captures from the former Central Powers who sold them for cheap in order to keep up with reparation demands

The Mosin did not garner international favour over the designs coming out of the factories in Oberndorf in Germany or Steyr in Austria. However, the Russians did sell some abroad, namely to Montenegro, Albania and Serbia. While Montenegro and Albania actually made it their official standard, Serbia kept them in the backlines until it was no longer possible due to the war.
Further deliveries to other nations such as Romania would occur during wartime. These "Balkan Mosins" come with a variety of different markings and slight modifications (such as ground imperial insignia) that have yet to remain fully uncovered.

After initial success against the Central Powers, the Russian Imperial Army would soon find itself on the defensive against counteroffensives by Austro-Hungarian and German troops.
Already early into the war, both nations acquired tens of thousands of Mosin rifles both from the Eastern and Southern Front where it was wielded by Montenegrin, Romanian and Serbian forces as well.

With all warring parties facing a shortage of rifles, these captures were pressed into service in the second line to free up as many main service rifles as possible. While the Germans distributed the rifles as they were, only adding a "Deutsches Reich" stock stamp onto the buttstock and occasionally marking the receiver with "Deutschland", the Austro-Hungarian ministry of war gave out detailed guidelines on how the rifles were to be adapted for use with their forces.

Adapting the sling attachements to allow for the carrying-style of the Mannlicher M.95 by means of adding sling swivels in the corresponding positions
Rechambering the rifles to the M.93 8x50mmR cartridge to ease logistical demands. These conversions are split into two types, where Type A would see the barrel bored out to accomodate the larger cartridge and relined, and Type B where only the chamber was re-cut. These are commonly called "squeezebore" conversions. As the action was capable of withstanding the higher pressure generated in these, it was likely done to speed up the conversion process further.
Restamping the rear sight for 200-600 Schritt (0.75m) and adding a Stutzen front sight post

Thanks to a very similar rim dimensions of the respective cartridges in service with the Austro-Hungarian and Russian empires, no modification was necessary on the bolt.
Not all captured Mosins were modified for the new cartridge as the captured ammunition supply proved to be sufficient later in the war.

The two minor powers in the central alliance would also use the Mosin in some quantity, likely provided by the German Army first and foremost.
These were generally left as issued, Bulgaria merely adding a stock stamp in form of a pinecone and the Ottomans only restamping the sights with Perso-Arabic numerals. Occasionally the sling attachment was changed, but this was not universal.