in our case it's mostly for that training and handling commonality thing still being followed from era of 1A SLR
but in terms of designs, charging handles are honestly perhaps least talked and underrated parts in firearms, and almost in all firearm designs I've observed it mostly comes out as a one or other kind of compromise
take standard AK for an example, reciprocating handle affixed on bolt carrier itself, now you have some plus and minuses like,
+ simplest, nonsensical design, maintenance free, easy and cheap to manufacture
+ doubles as forward assist, just slam on it if the bolt carrier on your AK didn't seat fully forward
- requires a slot in design as it moves along with reciprocating bolt carrier, opens up an AK enough for dust, dirt and all kinds of shits to go in the working parts like trigger group
- sticks out in perpendicular to the rifle, may get stuck in your gears or other stuff when moving around with it in your arms
- since its on right side, your regular right handed shooter may have to take his hand off the pistol grip to operate it (though it could also be seen as an accidental fire prevention feature in long way)
>so, compromise in terms of sealing of design, some handling and tactics things
take standard AR for an example,
> very first AR prototype too had reciprocating knob of charging handle on right side with big opening on bolt carrier side
> as the design progressed, priority shifted towards providing the most sealed design possible, so they first put it atop and that "carrying handle" atop that also acted as a shroud for charging handle for accidental bumping, eventually with second prototype of AR15 they shifted towards triangular T-bar design that further evoved as T-bar design of non reciprocating charging handle we all know
> some of early top handle prototypes did have some means to manually actuate bolt forward ala forward assist, those portuguese AR-10 used that, there was even some upward turning T-bar design with clamps like things to grasp on bolt carrier and use as some sorta forward assist, but most production level first pattern M16 sacrificed forward assisting feature for sake of simplicity (it's also a thing that first large scale AR-15 adopter was USAF ground personnel who might not have much idea about need of forward assist), only vietnam experiences made them to adopt side mounted paddle or button as forward assist device thing with M16A1
> so overall, T-bar comes with,
+ sealed design, doesn't stick out, simple design and manufacturing
- sacrificing bolt forward assist feature, but a dedicated device is added to right side for that, became standard
- an operator has to take his hand off pistol grip to actuate it BUT also his chin off from buttstock as it'd otherwise hit on it, though with bolt hold open one can bypass this operation
in case of INSAS pattern firearms
> they chose Kalashnikov design but adopted it around 1A SLR features
> design is sealed in right side (in kalashnikov standards), while left side has a dedicated charging handle just near the handguards
> charging handle design is taken from 1A SLR, it's affixed to a slot cut and long rod somewhat keeps it sealed upto acceptable levels, knob folds down when not in use
> some later designs like Amogh, JVPC, this 5.56x45mm Carbine (just name it something re I'm annoyed of writing it like this) also added a manual bolt hold open "button" there to lock it backwards
so this design has
+ training commonality, operational commonality
+ makes it sealed upto acceptable levels
+ position is such that an operator can easily use it without breaking his grip off pistol grip, and supposed to use his gripping/non-operating hand to use it, even in prone firing
+ doesn't go in way of gears and other stuffs much while moving around
- perhaps more parts involved here to build it on a firearm
- completely sacrificing bolt forwarding feature, but it already wasn't there on 1A SLR so...yeah, legacy of old things, our soldiers are trained to cycle their rifles to clear any malfunction
so it's not just some knob that racks bolt carrier on a rifle, it involves lots of design and operational characteristics
whenever i think about guns, charging handles often perplex me, makes me think deeply about various "what if..." scenarios like how changes in charging handle would affect a firearm and all...
I personally think simplest and least compromising design of charging handle out there was what russians did on their second and third prototype of original AK-12 (not current AK-74M with just top rails design originally named AK-400) - it had some Z shaped design that could be rotated around so with simple disassembly it can be made left or right handed, and that Z shape allowed for not having an open slot on sides as it could just cycle without touching main body - that sheet metal of body could just pass in that space between Z shape, and of course as a reciprocal design it could also double as forward assist
just observe yourself
View attachment 41186
but this design didn't pass Ratnik trials over some other reliability concerns like ejection angle problems, the gas piston had to have some opening between its stem for allowing passage for that top cover lug which made it fragile, but mostly Izhmash Arms met a fate similar to OFBs here as it got reconstructed into Kalashnikov Concern and this design was sidelined in favour of more traditional AK design that eventually became AK-12