uhhh, might want to review that link you posted.
The “1,000 round drum” is for an AirSoft gun. It shoots BB sized plastic pellets. If it held 1,000 rounds of AK47 ammo you would need a 2 wheeled cart to carry the gun and ammo around..
You are right. I just thought “If I post that the drums are 75 rounds, some one will come up with some mod drum with a gazillion rounds.” So I googled it. However, I could see mongo drum able to carry 1000 rounds, but it would probably extend out a ways.... and would have to be really bizarrely engineered with some kind of belt. I just bot a thousand rounds. If you had a drum big enough for it, it (the weapon) would have to be on a tripod, I guess.
Do you have a good source for 7.62, btw? Cheaper than dirt is on back order. Most places are sold out.