This comment will be based primarily on Sven-Eric Liedman's great biography A World to Win from 2015, and on Marx's own writings.

The passage you're quoting is from one of Marx's addresses to the Communist League, this one from 1850. But let us start talking about Marx and weapons, a little broader.

Marx went to university in Germany, or rather, in various German speaking cities. Liedman describes Marx's university years as rather in line with the norm of the times, with poetry and pranks. Marx loved both, and wrote quite a bit of romantic poetry, not to mention, is known to have kidnapped a goat. Ah... university! We all remember our first goat-napping. In the German academic world, there is a form of fencing known as "mensur", which was widespread particularly in the 19th century, but later evolved into a thorough bourgeois thing in the late 19th century, early 20th, with many famous right wing figures proudly showing their mensur scars. While Bonn university, where Marx started his studies, wasn't a university famed for mensur tradition, it isn't unlikely that there were a couple of mensur associations associated with the university. Other biographers do mention that, allegedly, Marx should have been involved in a duel in 1836, while enrolled at Bonn University. So a young Marx perhaps fencing, it isn't too far off, is it? The young student, nicknamed 'the Moor' by friends, and later family, would have undoubtedly look dastardly, sweeping and swinging at his enemies, wouldn't he?

There is however a problem... The young Marx didn't do military service, because of a condition described as a "weak chest." Marx was never much of an athlete. Even when he became a little more mature, while visiting his life-friend, comrade and confidant, Friedrich Engels in Manchester, it was clear from their riding trips, that not even riding, as a leisure, was anything Marx was fit for. He was described as looking like a sack of potatoes. So while the young Marx might have been the most clever young man in Trier, with the most beautiful young fiancée—Jenny von Westphalen was described as the most beautiful young woman in Trier by contemporaries, according to Liedman... and Marx of course, but I fear he may be biased in this regard—I doubt we would have seen Marx own a rapier, sabre, or any other such instrument of fencing. Not to mention, mensur isn't traditionally associated with duelling, and the above mentioned duel is contested by biographers.

Well then... What about the revolutions in 1848? Marx was alive, and in Germany, and oftentimes the conflict moved close around Marx... But unlike Engels, who had received military training at the Prussian Officer school, as an artillery officer, and hence was nicknamed 'the general', and who participated in fighting at the front lines multiple times, Marx is never known to have picked up any other weapons than the editorship of the Neue Rheinische Zeitung. An editorship that became dangerous enough, that the Prussian censors tried shutting it down, and even prosecuted "Doctor Marx", as his title was, following the revolution... but again, not for firing any form of firearm against the forces of reaction.

Marx then had to leave Germany—again—and never really settled anywhere before London. In his dear Paris, we have no indications of Marx going to the salons strapped, and in Brussels, where Marx stayed shortly, no indications of armament was found. So the Marx family settled in London, first in Soho. In this working class part of town, the family went through its hardest struggles; harder than when they were expelled from Paris. Money was tight, and no doubt, had Engels not used his job in the family business, to grant one loan after another to his friend and comrade, the Soho bakers, butchers and their landlords, would undoubtedly have found a way to use weapons against Marx. They were in dire straights, until the day Marx finally got his inheritance. But I am speeding ahead.

The passage you're quoting, is, along with "The history of all hitherho [...]", "The philosophers have only interpreted [...]", "Religious suffering is [...]", perhaps one of Marx's most famous quotations. It was in an address to the Central Committee of the Communist League, delivered in March of 1850—another famous one was delivered in July of the same year—but in it, Marx does not mention anything about carrying a pistol in his inner pocket, or anything other like that. Marx, as an intellectual, and a person without any form of military experience or knowledge or training, what-so-ever, wouldn't be at the frontline. He had had his chance, but opted against it, since he knew he wouldn't be of much use to a revolutionary detachment. All that Marx knew about war, and all references we have in Marx's works about war or militaries, or anything of that nature, were run by Engels first, to ensure some form of expert oversight; Engels who loved everything weapons and war and military, kept reading up on it, even after not being in service any longer. Not to mention, allegedly being an avid and talented hunter.

Back to the inheritance. When Marx finally received his inheritance from his father, which his mother had kept from him—possibly out of spite, possibly fearing he would squander it up; Marx was never good with money, famous, or infamous, for living well above his means during his student years, it was Jenny who controlled the wallet in the Marx home—the Marx family moved out of the Soho apartment, and to a nicer row house with a small garden in Kentish Town... but this move up doesn't carry any new evidence of the ownership of arms with it. I personally don't think that Jenny would have allowed the money to be removed from the budget, if Marx had even asked, which I also doubt.

That said. All wasn't good in the Marx family. As most poor families living in London in the 19th century, diseases were a part of life. Jenny was near death many times, Karl was also often tied to the bed. However, the reason I bring this up, is because of the kids. Jenny and Karl Marx had 7, though only three lived to adulthood. 'Guido' Marx, the second son, lived to be just over 1 year. He died in 1850. His death took a hard toll on the family. Shortly after Guido's death, the daughter 'Franziska' was born, but lived only just over a year as well, she passed away in 1852. These were dark years for the family. The first son, nicknamed 'Musch' became Karl's favourite son. 'Musch' was a charmeur, and an inventive kid, and even helped stave off the creditors by giving them false information at time. At age 8, Musch passed away. This was in 1855. Marx was, according to friends, disconsolate. He became deeply depressed, and may have even, at times, considered suicide. Jenny, Jennychen and Laura, might have been the three threads keeping him to this world. [And had Marx tried at suicide, it isn't unlikely that it would have been by gun; to emulate the suicide of the young Werther, from Goethe's famous work. Goethe was, after all, Marx's favourite poet.] All in the brackets, is however speculation.

So, with that small bit of speculation, and a very dark note to finish on, let me conclude:

We have no evidence that Marx ever owned any weapon, nor walked around armed. Marx wasn't an athlete, he wasn't a hunter, he wasn't a soldier, he wasn't a highwayman. Marx was a theorist, a journalist, a revolutionary, a historian, a philosopher, a father, and much, much more... but a gunslinger, he was not. He must however have been at least in indirect and peripheral context with weapons and armed folks multiple times.

Thank you for your time.

---

Works cited:

Liedman, Sven-Eric. A World to Win. 2018. Verso.

Marx, Karl. Early Writings. 1975. Penguin Books.

Marx, Karl. The Political Writings. 2019. Verso.

Various letters from the MEGA, which I have my own extracts from. I will look for the proper places, if interested. It is mainly to do with the monetary and the deaths of the children.

Marx in his younger years was heavily involved in harassing and combating Prussian nationalist groups - notably the Borussia Korps. As a result he carried a pistol for defence and even engaged in a duel with a member in 1836.

Nicolaievsky, Boris; Maenchen-Helfen, Otto (1976) [1936]. Karl Marx: Man and Fighter.

Though I can’t find the documentation at the moment, though I’m confident I’ve seen something of it at some. His exile from Prussia, and it’s speculated his later exiles from Brussels and France were for similar reasons, was caused more so than from his public call for arms but also because he physically bought knives or blades to arm different workers struggles.

His later years while based in England though are more personally tame and focused on organizing armed militants and the ideological development of organizations rather than personally being a combatant or direct conspirator in the acquisition of arms. But still he had a portion of his life where he was directly being combative himself.

Given that, I don’t think it’s documented how he was armed later in life. I think it’s safe to assume to had weapons in his house and was prepared to defend himself but we don’t know what that would be.