I have been messing around with Lr308's for a couple years, and there isn't much I don't know about them. However one thing I can't figure out is why do the LR308 Bolt carriers have now forward assist tracks on the side? What I mean is if you buy a new bolt carrier from dpms, midway etc.,(LR-308) only one option is available for the carrier. It has no tracks machined in the carrier. The only guns from the factory I have seen that have these are the SASS and AP4 that I have put my hands on. Most of the smooth side uppers do not have the tracked bolts, which is understandable since there is no forward assist knob. But when I purchased my dpms factory A-15 smooth side 5.56 bull,( no dust cover or forward asist) its bolt carrier had tracks, which allowed me to swap the upper receiver to a bcm and have a functioning forward assist. They make the the dpms factory LR308 upper with dust cover and forward assist so you can build what you like from it, but do not sell the bolt carrier that will work and have a functioning forward assist. Basically you have a forward assist knob but it doesn't function. Somebody know the answer to this or can enlighten me on the this? Or how do you get ahold of the factory bolt carriers with the forward assit tracks used on the sass or ap4 LR308?