Why Soviets hated PKM tripod?
As many of you know, PKM was not just a stand alone medium machine gun, but actually a whole family of all purpose guns. This would include tank version - PKT, armor carrier version - PKB and, as the name of the article suggests, version on the tripod - PKMS. In this case, the letter "s" stands for "stankovy", which can be translated as "on a tripod".
So how come we almost never see these PKMS neither in action nor on photos from training?
Couple of words about the PKM and its tripod
The PKM is a further development of the PK machine gun, which, in turn, was designed to finally unify the whole family of light, medium and heavy machine guns. The idea was the same as it was for the MG-34 family of machine guns - to have it all in one. Bipod, tripod and vehicle mounted versions were supposed to have the same base.
After the Second World War, Soviet's had DP-27 machineguns, as the light machine gun. They were phased out by the further development of it - the almost mythical RP-46. But the army also required a mounted machine gun, which was supposed to cover the heavier support role of the sustain-fire machine gun. The old Maxim gun and SG-43 machine guns both did not satisfy the army. Maxim was too complicated and heavy, while SG-43 had its fair share of problems with reliability.
And so the requirements for the general purpose machine gun were born. And Kalashnikov with his team managed to deliver such a machine gun.
PKMS or PKM on a tripod
As there were two version of Kalashnikovs machine gun - PK and PKM, so there were two version of tripods. Both guns had unique tripods, yet they were unified and can be used between each other.
PK was equipped with heavy and robust tripod, named after it's designer - Samozhenkov. This tripod was had around 8kg of weight and could provide very steady shooting, when placed correctly.
The PKM, which was designed and adopted shortly after the initial adoption of the PK, had it's own tripod. This one was designed by Stepanov, and received his name. This tripod was significantly lighter. As well as the PKM itself. The machine gun weight was only 7.5kg and the tripod weighted additional 5kg. This whole setup was lighter than majority of other machine guns in the same class.
So, in theory, such a light piece of equipment should have been used extensively, because it is just so easy to carry. For example, the tripod for the MG-3 weights around 15kg, so it is hardly man portable. Yet, in practice, Soviets and their descendants hardly ever mounted their PKMs on the tripods. And there are good reasons.
The problems with the tripod
The first problem is associated with the main advantage of the PKM tripod - the weight. While being very handy to carry around, it simply does not provide much stability because of its lightness. While there was some increase in MOA when shot on the range, the combat situations were, of course, different. But we will get to them later.
Second problem was the construction of the tripod itself. It did no allow full circular rotation of the machinegun, when installed for land usage. The narrow adjustments were simply not enough to make much sense of the tripod - soldier would have to move the whole setup if he would need to shoot further at the right. And while it was not hard to do due to the lightness of the setup, it was just not making sense. The bipod was providing similar stability.
Another problem is that it takes place. In theory, the tripod would make the best use when in an entrenched position, like a pillbox. And these are usually really tiny, at least if built correctly. The PKM on a tripod takes way more accommodation place and is just too massive to operate in close quarters.
The doctrine for PKM
Now, all these problems mentioned in the previous paragraph might be true for wartime, after some practical experience is gathered. The PK was adapted way before soldiers could get their hands on it in an actual combat. This raises a big question, which I do not have a good answer for. Why we see little to know photos or video footage from training exercises, featuring tripods?
The training manual for the PK family of machine gun features a number of images, explaining how the machine gun should be used, when in the mounted configuration. So, at least in theory, these should have been trained.
PKM on tripod at war and summary
So far, there is no good theory to why PKM was so rarely used on a tripod during training exercises. All in all, Soviet Army was following manuals and orders more often than not. But it is interesting to compare the doctrines and practices of Soviet Army and its Western counterparts. The majority of NATO forces would rely on the mounted machine guns as on one of the most powerful section firearms. However, grenade machine guns were rarely deployed in the tripod setup, usually being installed on the vehicles. This was vice versa for the Soviets - while ditching mounted MGs, they really liked to carry AGS-17 GMGs around. However, this would not explain why Soviets didn't use PKMS as GMGs became a thing a decade later.
The peacetime practice of not using tripods was carried to war in Afghanistan. While there is a number of photos of the tripods, it seems that they were made for show off and were not really used. The exception would be the usage on the outposts, yet, it is not that easy to find much photographic evidence to support this. When on actual mounted or dismounted operations, tripod made little sense as the PKM fire is just as accurate and devastating when fired from the bipod.
The notable exception for the rule would be the Soviet Border Guards. There are more photos of the tripods in use with the Border Guards. If you think, that this is because they were always stationary and just observing the border - think again. The actual reason might be the fact, that this branch of forces was more disciplined and would follow the book more often.