As Russia got more involved in the Syria fighting and supplied more military supplies and ammunition for the Assad forces an old problem became an issue once more. Russia still cannot manufacture ammunition that is as reliable as what is generally available in the West. Russian ammo may be the cheapest around, nearly as cheap is the Chinese stuff and it is usually of higher quality. Since China adopted Western manufacturing standards during the last three decades their ammo quality has improved a great deal.
Russian munitions manufacturers were able, or willing, to adopt Western manufacturing methods. This would have involved a large investment in new equipment and training the workforce how to use and maintain quality control. So Russia kept producing the usual stuff that was the cheapest and still least reliable stuff available. Experienced users of Russian ammo knew what to look for before loading the cartridges. Poorly attached primer meant the cartridge was tossed aside. Obviously malformed cartridges cases were also rejected. That eliminated a lot of problems, especially for pistol ammo. A lot of the foreign buyers knew how to check Russian ammo and enough of that knowledge spread to new customers to make the cheap Russian ammo selling.
Russian machine-gun, rifle and pistol ammunition is still produced in large quantities but it does cause problems for new users, especially if they are headed for a combat zone. During peacetime, the lower quality and higher failure rates of Russian ammo is not a major problem. But in wartime when a lot of it is being used it can become an issue. During training a jammed or exploding rifle or machine-gun is something that can be dismissed as a rare event. Jammed rounds provide a teaching moment and work for unit armorers. Exploding rifles, often because a bullet got jammed in the barrel and the next one causes a lot more damage, sometimes including parts of the weapon getting loose and hitting the shooter or anyone nearby. In combat these malfunctions can be disastrous and, at the very least are bad for morale. Other quality problems, like cartridge cases not built to specifications and failing to load or extract were not fatal in themselves. But jams like this in a firefight could be fatal for other reasons.
Another problem with the low quality ammo is that it is not consistent when fired. That means much less effective for snipers and any troops who depend on accurate single shots. That was why automatic weapons for the infantry were so popular in Russia. During World War II Russia manufactured millions of sub-machineguns (like PPSh) firing 7.62mm pistol ammo. Ammo quality was not an issue because weapons were used by many troops at once and one or two out of several weapons failing in a battle was not a major issue. This led to the AK-47 after World War II. But even there, the ammo quality eventually became an issue because the AK-47 used a shortened rifle cartridge that was more powerful and being used in a weapon often fired on full automatic.
These problems became obvious to the West after 2001 when Iraqi and Afghan troops eventually became eager to switch from AK-47s to M-16s because of problems with ammunition quality. AK-47 ammo has long had quality issues, at least to a greater degree than M-16 5.56mm stuff. As new Iraqi and Afghan security forces were recruited, trained and sent into action, there was a huge increase in demand for AK-47 ammo. This led to a lot of older stuff coming onto the market. In many nations that use the AK-47, including China, not a lot of ammo is used. Put simply, the troops don't get a lot of practice firing their weapons. But large stocks of ammo are stockpiled in case there is a war. With the increased demand from Iraq and Afghanistan, many nations with these stockpiles saw an opportunity to unload their older (often 40 years or more) stuff. This elderly ammunition was not only suffering from the usual aging problems of old ammo (the chemicals in the propellants breaks down and makes the bullets move a lot slower, and less effectively), but often showed the effects of poor storage (corrosion). All that, plus the ease with which one can bribe Iraqi or Afghan supply officials to accept the bad stuff, led to many Iraqi and Afghan troops going into battle with very defective ammo. These problems largely go away with M-16 ammo, which is made to higher standards in the first place, and rarely lies around for a long time. M-16 users let their troops practice more often. There is some crap 5.56mm ammo out there, but to a much lesser degree than is the case with the AK-47 stuff. Iraqi and Afghan troops figured out that their chances of surviving in combat improved considerably if they were using M-16 type weapons, even if these rifles required more frequent cleaning.
While it was useful to have everyone one on the same side using the same assault rifles (AK-47s and M-16s sound quite different in combat) there was another solution available. As surplus AK-47s and SKS (semiauto rifle using AK-47 ammo) weapons became widely available in the West after the Cold War ended the market for Western quality AK-47 ammo grew. The military was also a major customer because SOCOM (Special Operations Command) often used AK-47s on missions or had to supply American made ammo to allies who did. The Russian weapons could also be built, to higher quality standards, by Western manufacturers but that was not as important as getting higher quality ammo. The AK-47 ammunition built to Western standards had far fewer failures (not firing at all or jamming the barrel with stuck bullet) and user injuries (low quality shell casings that allow the propellant to vent some of the high-pressure air back against the bolt). The Western style stuff left less crud in the barrel and was more consistent in performance. This encouraged more users to use single shots, not bursts of fire (spray and pray).
There were many benefits to better quality ammunition in general. Not only was the weapon instantly more accurate and consistent, it was also less prone to failure but it also required less frequent and thorough cleaning. Even AK-47s lasted longer when using quality ammo. In Syria American allies, especially the Kurds, benefitted from getting quality ammo. That made the Russian weapons many Kurds used more effective and that was also great for morale.
Troops still supplied with Russian ammo, including thousands of Russians and civilian contractors complained about the poor quality of Russian ammo. Russian snipers were often supplied with Western made ammo otherwise the accuracy and effectiveness of these snipers declined quite a bit. That was one reason why Islamic terrorist groups, who often had some decent snipers, were never as effective as they could have been. It should also not underestimate how useful it was for Western troops to have their opponents using the bad ammo that would often be a lifesaver for the Western troops.