They aren't refered to as 'banana magazine'.
People will laugh at you for saying that. Not to be rude.
But some hold 20, some 30.
When Armalite first produced the AR-15, the magazines were straight walled. This limited the capacity to 20 rounds, as the taper in the cartridge case would cause feeding problems. To counteract this, the "banana magazine" as you called it was produced. In USA conversation, this term is not generally used, but has been used in the media and some movies. 20 round magazines today are still straight walled.
I think you are talking about the STANAG magazine, which holds up to 20 rounds
Lots.
There are 20 and 30 round magazines. some even 10 rounds There is also a "BETA Mag" that holds 100 rounds. It uses to drums of ammo that attach underneath it. They are heavy and only used for mounted m16's or over watch duty.
46x53 nado
The weight of an M16 rifle without a magazine or sling is approximately 7.2 pounds.
No
The M249 is typically fed from a belt... 100 round "nutsacks" and 200 round plastic drums are often used. It can also be magazine fed from STANAG 4179 magazines (the type used in the M16 and several other rifles). Those can be whatever capacity they're manufactured for, but 30 rounds is typical.
sports illistrated
Yes
It depends strictly on the magazine. Some magazines hold 10 rounds, some hold 30 or more.
The SKS packs a bigger round (7.62mm) than the m16 (5.56mm) but the m16 has a higher magazine capacity, better accuracy,and a higher rate of fire, so the SKS is more powerful, but the m16 is generally regarded as a better weapon.
magazine
roughly one pound, when loaded