I cannot confirm the use of muskets in the 1950-9 Invasion of Tibet. In fact, it's one of those propaganda pieces that gets way overblown, Polish cavalry style. Scorcese's Kundun (or was it Brad Pitt's Seven Years in Tibet?) actually filmed a scene of the Battle of Chamdo with the Tibetans shooting arrows at the People's Liberation Army.

Ok, so to back up and reiterate: I cannot confirm that these things didn't happen. Without video evidence, it's impossible to deny. I'd also say that what constitutes "use in warfare" seems a bit ambiguous to me.

Either way, I can explain a bit regarding the state of the Tibetan army in the 1950s and the use of muskets.

Tibet had never been a particularly formidable military power since the fall of the Empire in 851 C.E. When the Mongols invaded, they became Tibet's primary military partner (both defensive and offensive) operating wars in Bhutan, Ladakh, and even as far away as Persia. When the Manchu took over China, they gradually assumed responsibility over Tibet, until basically invited into a full military occupation in the 1790s when the Gorkha (Nepal) invaded Tibet. After that, the Tibetans had a bit of a push/pull relationship with the Manchu, grateful for the defense, and especially happy to be under the rule of Buddhist monarchs who were quick to support the Tibetan Sangha, but not so happy about the secular aspects of rule like the Ambans who essentially had dictatorial control over the country, and executed political criminals essentially at will. Constant uprisings in Tibet pushed the Manchu to fund the Tibetan sangha. More money meant more monks, more monks meant less of a fighting-age male population.

During the Xinhai Revolution of 1911 that began the Republic of China, the Tibetans had their own revolution focused in Lhasa. Sam Van Schaik's Tibet: A History doesn't mention too many guns, but he does talk a lot about tunnels and bombs being used to prosecute what seemed like some bizarre combination of urban warfare and terrorism. Presumably there were guns and swords used as well (swords have been used as honorofic symbols of governments position and power in Bhutan for many years, though while it's a stretch to say their use in Tibet was similar, it's not like there haven't been a lack of swords in Tibet in either case. Primarily ceremonial, they don't need to be razor sharp in a cramped basement to cause serious damage).

There was also a large minority of mixed-race young men in Lhasa at the time: men whose fathers (paternal ancestors in general) were of Chinese (or Sikh) descent and whose mothers were Lhasa Tibetans. It's a rather common historic Asian tradition to follow in the father's footsteps, oftentimes limited by law (such was the case in Europe, and a similar example can be found among both potters and gunsmiths, including among Europeans who were stranded in Joseon Korea c.1680 who were immediately relegated to the gunsmithy and were required to remain there when not being called to the capital). These young men, relegated to the lives of soldiers, spent most of their days performing the lion dance for cash, while presumably spending the rest of their time maintaining their equipment or waiting for some kind of orders. I don't have a primary source, but it's reasonable to imagine that they saw some combat at this time (as suggested by Shakabpa's book).

After the Revolution, the 13th Dalai Lama, who prosecuted the war primarily from a position of exile in India, returned to Tibet and drafted Tibet's Declaration of Independence, saying that the relationship of priest and patron between the Manchu and Tibet had "vanished like a rainbow in the sky." (Note how no mention of a prior, existing, or future relationship with China or the Chinese is mentioned). But to maintain Tibet's independence, the 13th Dalai Lama knew that Tibet had to modernize if it were to keep up with China and India, her primary rivals/potential partners.

The Dalai Lama's modernization efforts included opening up an English-speaking school, sending off four boys to a boarding school in the United Kingdom (to sadly little ultimate effect, but it did lead to electric lights in Lhasa's streets), sending for radio operators who might help connect Tibet telecommunicatively to the world, to reform the tax code, establish diplomatic relations abroad (issuing passports that were proudly accepted in America, Hong Kong, and across Europe, see Shakabpa), and most controversially, modernizing the Tibetan Army.

Now, backing up. The Tibetan Army at this point consisted of what we would otherwise call levies. Tibet ran on a sort of feudal system, with governors responsible only to the sovereign in Lhasa, who tried to coordinate the lords, landowners, peasants, and monasteries in their territory. It was the breakdown in negotiations with both Lhasa and Beijing (led with a profound Russo-phobia) that led to the British to invade Tibet under Sir Francis Younghusband in 1904. Younghusband invaded Tibet with his fully modernized British army, complete with Maxim machine guns. The Tibetan army, made up of levies, fought back with swords and muskets. The 1904 "invasion" in usually referred to as an "expedition" and probably part of this nomenclature has to do with the comparatively small bloodshed that took place. The Maxim guns were used in an event on 31 March 1904, now called the "Massacre of Chumik Shenko." The Tibetans agreed to surrender and allow the expedition force to pass, but in the process, it was considered a bad idea to have the Tibetans at their back, fully armed. So the disarming of the Tibetan force began.

To the British, their weapons were tools of the military that were issued to them by His Majesty's government. To the Tibetans, their weapons were personal posessions, marks of status, rank, and wealth. For some of them, it was probably the most valuable possession in their family. When the British army tried to disarm the Tibetans, a language barrier prevented a peaceful exchange, one Tibetan attacked a Sikh soldier, and the misinterpretation of the event ended in a massacre of some 800 dead Tibetans and 12 wounded British.

Keep this in mind, it'll be important in a second.

Fastforward to the post-1911 Revolution. I'm kind of skipping over a lot while trying to stay on point.

The Dalai Lama's modernization of the army involved getting support from the British and Japanese. It probably seems weird, given that I've just outlined a British invasion of Tibet, but Britain's whole goal was to secure Tibet as an ally against Russia in their Great Game. Once those trading rights were secure, Britain and Tibet became fast friends. British officers and Japanese officers were brought to Tibet to train the Tibetan army, ultimately it would be the British way that would stick. The current Dalai Lama says he remembers leading his troops in their morning drills, giving the hand motions and commands inherited from the British officers. Also inherited from the British was the tradition of flags to represent regiments. One of these flags became the unofficial Tibetan national flag, and is currently the symbol of Tibetan national independence.

What had to come next was the modernization of Tibetan military technology. Even with a standing army, the Dalai Lama was certainly aware, arming them with 18th Century technology was a losing game no matter how disciplined and trained the army would be. She began reaching abroad (primarily to British India, mandated to be her basically only trading partner) to acquire weapons. Small arms, were obviously a primary goal, but there's some obvious evidence that larger arms were acquired, though I have to say I don't know any specific technical details (though keep reading and it'll become evident that they had more than just rifles). It's claimed that these weapons were acquired from the British, but Japanese monk Ekai Kawaguchi relates in his Three Years in Tibet that upon looking inside crates of weaponry, the words "Made in the United States" were written on the guns. (Though I don't see why it wouldn't be possible for guns to be manufactured in the United States and resold through an Indian-based supplier. I frankly don't know enough about the economics and business practices of the firearms industry in the early 20th Century to be able to say.)

1/3

There's a few reports that are difficult to confirm due to the fact they naturally take place in some of the most back of beyond parts of already isolated and war-torn countries. The two that you most commonly hear would be the Soviet-Afghan war of 1979-1989 in which it is claimed that some members of Afghan Mujahideen factions were occasionally seen to use Jezails, a traditional long barrelled flintlock weapon that could be made as a smoothbore musket or rifled weapon. Similarly I've heard claims that Tibetan independence fighters during the PRC's invasion of 1951 and the following decades of insurgent activity sometimes used matchlocks which are a traditional hunting weapon in the region. In both bases these are difficult to confirm and possibly propaganda to play up the backwards nature of the enemy they were fighting.