To those new to firearms, there are some counter intuitive realities you must learn, which are different from pop culture myths about famous rifles. After knowing the basic, you will realize why exactly the IA chose the direct impingement version of the Sig and how good the decision was.
The first thing to unlearn is that the M4 i.e AR 15 platform is "not reliable", or that AK 47 is "the most reliable rifle in the world".
View: https://www.youtube.com/watch?v=YAneTFiz5WU&ab_channel=InRangeTV
View: https://www.youtube.com/watch?v=DX73uXs3xGU&ab_channel=InRangeTV
As you can see here, the AR 15 platform is quite reliable and shows better results in mud tests than the AK. This is contrary to the stereotypes that "you can do anything to an AK it will keep firing" which our internet experts and even some IA officers throw about. On the other end "M4's are delicate, they're not reliable, only for special ops etc" must also be unlearnt.
To witness an even more counter intuitive example, here's the German G 36 performing better than the AK in the mud test. The G36 like the AR 15 has a closed system which normally doesn't allow mud to get in. It also uses gas piston like the AK and most other rifles. Most of the controversy about the G36 has also been proven false recently. But that's another topic.
View: https://www.youtube.com/watch?v=t2dU-AH0aQA&ab_channel=InRangeTV
The reality is that the AR 15 platform, which M4 is part of, is one of the most reliable systems in the world due to its internal design. The primary contributing factors is its dust cover and closed system, which prevents mud and other debris coming into its system in the first place. And when they do get into the internal system, that's when its direct impingement system plays a role by sending gas back into the chamber and blowing out any mud and dust. The direct impingement system on the AR platform also has the advantage of giving less recoil and lower weight, especially relevant for the Sig 716i, since it uses a large calibre.
To understand why the M16 and M4 falsely got their reputations as unreliable, watch the video below. Basically American public ordinance babus in the 60s intentionally gave faulty ammunition and didn't give cleaning kits to make the M16 look bad because they wanted to produce their old M14s.
View: https://www.youtube.com/watch?v=NYar4Zf8jH8&ab_channel=SmallArmsSolutions
The AK series are also very reliable in its own right, but does not deserve the endless praise it gets in pop culture and casual analysis on the internet. They're rifles like any other and get jammed like any other, in some cases more than western rifles. They use the same gas piston mechanism that most other rifles do, so they're not doing anything unique.
To understand the difference between direct impingement and gas piston, watch the videos below of the different mechanisms of the AR vs AK platforms. Gas piston was thought of as more reliable, but there is serious doubt on that claim now considering how reliable direct impingement is. Gas piston also increases recoil, due to a solid metal bar violently pushing the bolt back, compared to gas piston which only has gas coming back.
View: https://www.youtube.com/watch?v=omv85cLfmxU&ab_channel=MattRittman
View: https://www.youtube.com/watch?v=_eQLFVpOYm4&ab_channel=MattRittman
Finally, people don't realize that the quality of the magazine plays as much of a role in the reliability of a rifle as the rifle itself. The magazine is the component that feeds rounds into the rifle, and hence must function flawlessly in its spring system.
The IA made a very smart choice by going for the direct impingement option for its Sig rifles and choosing an AR platform to begin with. Now, why the INSAS has been such an unreliable rifle is another discussion, and mostly to do with quality control in sarkari babu OFB. But with this post I want to give people the basics of modern service rifles and break common myths.