Difference is in kind of gas pistons arrangement used in both,
AK-107 (i'd like to mention here AK is not
Avtomat Kalashnikova = Kalashnikov's Automatic but
Aleksandrov/Kalashnikov = Alexandrov/Kalashnikov's, named after a junior engineer Yury Alexandrov who worked in then Izhmash plant, designed this pattern of counter-recoiling mass system but used AK pattern rifle to implement it, so yeah) one uses two separate pistons+two separate recoil springs (and of course dual-venting gas block to provide push to each oppositely facing pistons) interlinked together sorta system, syncronised using a set of rack-and-pinion mechanism
View attachment 98243
1 = bolt carrier with recoiling pison, AK style long storke one in essense
2 = recoil spring of number 1, very much AK styled
3 = Counter-Recoiling Piston + circular rack-surace on it
4 = Return Spring pf number 3
5 = pinion mechanism for interlinking number 1 with number 3, having circular gear/pinion, housed inside this H-shaped block
6 = U-shaped mount to affix everything in place, number 5 sandwiched between number 1's gas piston+rack surfaces below and number 3's gas piston+rack surfaces above, everything affixed on number 6 mount
7 = NOT A GAS TUBE but
Π - shaped Top Cover to cover number 1+ number 5 + number 3
sandwich mounted on number 6
8 = another Top Cover, this one is very much AK styled as you could see it
9 = double-venting gas block, T-shaped, vents gases on opposite top sides that impinges upon pistons attached to number 1 and number 3 in respective sides etc
AEK-971 (Avtomat, Yedinyy, Koksharov = Koksharov's common rifle) or its current version A-545//A-762 (number denote calibers) system is simliar in operation but differs only in the way recoiling-counterrecoiling set of pistons are attached,
Here instead of having separate recoil springs attached to each pistons and a double venting gas block Koksharov utilised single but larger gas block that is given opposite facing gas tubes on its top and it vents from middle, at a place where there is this collar-piston that is recoiling part (attached to bolt carrier) and a counter-recoiling piston interlinked with collar-piston (by extension the bolt carrier too) via inside-housed rack-pinion mechanism.
View attachment 98241
A-545 disassembled, notice number 1 denoting larger gas block which has this opposite-facing gas tubes attached on it ( number 2(X) is just showing end of gas tube for counter-recoiling piston, there isn't any gas venting happening here it's just a mechanical linkage with front iron sight block)
View attachment 98238
AEK-971's bolt carrier (sorry for lack of high quality pic of A-545 one but both are very much similar firearms), number 1 showing recoiling collar-piston attached to bolt carrier, very much AK style except it's hollow one housing counter-recoiling piston that is number 2 and there is this mechanical arrangement of rack-pinion inside, number 3 showing the moving linkage of pinion, you could also see those notched-rack surfaces below
So when it is fired, gases vented from middle impinges upon both pistons, one is recoiling backwards (collar-piston one) and operating working parts of bolt-bolt carrier etc while at same time other ( attached counter-recoiling one) moves forward, effectively eliminating recoil and so,
Now, advantagesdisadvantages parts of both, of course + is advantage and - is disadvantage,
Alexandrov/Kalashnikov one
+ relatively simpler working than Koksharov's as separate pistons interlinked with external rack-pinion set is easy to work with
+ disassembly is having extra step of removing counter-recoiling piston but is still very much AK-like
- since it's an ope system (and has that larger AK style ejection port) outside gunk sticking on rack-surfaces of the interlinked working parts could cause jams
- requires extra spring for counter-recoiling piston
Koksharov one
+ Primary Disassembly is very much AK like, you don't need to remove counter-recoiling piston unless required
+ Since rack-pinion set of interlinkage is practically housed inside the gas piston (albeit rack surfaces on top-bottom still exposed) there is less chances of outside gunk going inside and clogging them, although still somewhat susceptible to it
+ Doesn't require extra spring for working of counter-recoiling piston due to its design
- if shit goes inside and you needs to clean up rack-surfaces inside the bolt carrier etc, you might need some proper brush and something i mean just look at it disassembled further
View attachment 98246
so you see, you might need a longer brush to scrap off shits accumulated inside collar-piston's cavity or worse thing, if that small cross-pin of pinions-set gets lost or breaks then entire mechanism fails
So yeah, this is some basic technical explanation of their working,
i wish there was some way to demonstrate it all in some video or animation
but am not that much talented to create such things, also very much limited in terms of
resources
having said all these there is also another common complaint about such systems, that is since after pushing the pistons gases are vented out from middle section of the rifle (being more near to a shooter's face) many soliders testing these kinda weapons complained about hot gases venting out on their faces causing discomfirt, or overheating handguards more quicker than a regular AK
^This is applicable to both Alexandrov/Kalashnikov design and Koksharov one
So yeah, both designs have some plus and some minuses
As of now, Koksharov's design is selected for many Gendarmarie pattern units of Russian Armed Forces in both A-545 and A-762 designs, full production was supposed to start in 2020 but after
choyneez virus scamdemic am not sure what is current status,
while AK-107 design is also being tested and adopted by some small units, some Kazakhstani units also obtained about 100 of them and so,
.. Utter crap if looked from a purist's pov
