Eagle AR mags, and Ramline pistol mags both have what are called "constant force springs". These are strips of metal that coil up. They run down the side of the mag, and roll up under the follower. There is a lot of friction between the coiling strip and the follower. Another problem is this:
In a normal magazine, where there is the most ammo loaded, the spring is highly compressed and exerts the most force. Good!
In a mag with constant force springs, when there is the most ammo, and thus, the most weight pushing down, the spring still has the same force as when almost emplty. These springs have difficulty lifting all that ammo, and when combined with the friction, the problem is worse.
If you download them somewhat, they work smoother.
Duh, I would rather have a USGI mag.