Magpul PTS Masada 5.56 Lower Receiver. Available in Black and FDE, these will allow you to swap from the AKM 7.62 lower to the more user friendly 5.56 version.
Includes magazine release buttons left and right, front and rear pins, fire selector left and right including inner gear cams and bolt release switch. All you have to do is switch the gearbox over. 2 minutes and your ready to rock with an M4 magazine!