Well...
A Chinese made AK, all polymer (heavier than wood), with a fully loaded 100 round drum magazine weighs 15.5 pounds, not 40+ pounds.
Romanian SAR1 with a milled steel receiver, full polymer stock and furniture, original trigger group (also milled), steel gas piston, with a 100 rd. stamped steel drum mag and 100 rd. of 125 gr. FMJ lead core ammo weighed easily over 40 lb.
You can quibble over models all day. I’m basing this off of my experience firing this specific rig. I’m not saying they’re all going to be the same.