"This metal magazine came standard with the VFC HK 416. One of the best clips on the market. No need to wind this high cap mag on the field.
Pour the BB's in. wind it with the wind tool before the game starts and you're all set. No need to wind the clip again until you dump the entire mag. However, I think the magazine will not shoot the last few bbs due to this amazing "prewinding" function, not a big deal. It has trademarks if you're into that.
To be clear, normal high cap magazines need to be wound up every 40 to 50 shots regardless of the capacity. With the HK mag by vfc you only wind once with an allen wrench like tool provided with the magazine and it will dump 300 bbs before needing to be reloaded and wound up again. This also elimates the need for an external winding wheel for a more realistic looking mag if that's what you're going for.
This clip should fit in most m4/m16 models. It fits in both my M4s, my M16 and my HK 416. All of which are different brands.