actually from the basic operating mechanism POV,
PK, M249//Minimi and Negev are exactly same, all of them are AK-like open bolt machine gun systems and you can cleary see it in their bolt carriers,
PKM
View attachment 108599
M249 (MK48 and so)
View attachment 108600
Negev NG-7
View attachment 108601
and this commonality again came from same thing, i.e. using different AK variant as base and turning out an open bolt fixed firing pin machine gun outta it,
in case of PK it was AK, of course,
in case of Minimi/M249 it was FN FNC,
and in case of Negev, it was Galil (although not directly based but still),
just observe bolts on all these 3 and you shall see the signs of it
^So yeah, all 3 of them are more or less similar in performance,
major difference comes in how they feed as all 3 have different feeding mechanisms on them,
with PK being notable example of feeding from a claw-shaped round grabber due to 7.62x54mm is a rimmed cartridge and cannot be pushed forward from that belt,
while Negev in 5.56x45mm configuration has dual-feeding mechanism (not on NG-7 though) and they decided to make it magazine fed from bottom side hence they made this 'channel' like bolt carrier to accomodate magazine,
FN one otoh is simplest of them all, just FNC pattern bolt and bolt carrier turned upside down and magazine is fed from angle at other side,
^^We, OTOH, never experimented much with INSAS to say, make a belt-fed version outta it, something akin to FN Minimi//M249 at least
as i mentioned above, NG-7 doesn't have magazine fed feature on it only 5.56x45mm version has it,
and NG-7 and PKM are essentially same stuff so not much difference in terms of basic performance there...