Hey all, I'm new to this forum and want to begin an AR build. I have been looking at spikes and rock river lowers mainly. Today I was on aimsurplus.com when I saw the R guns anodized lower thought it was kind of cool. http://www.aimsurplus.com/product.a...n+AR/M16+.223/5.56+A3+Receiver+Set&groupid=11 I was wondering the what the difference between the R Guns lower and the spikes lower is. Does the R guns just have more to it (EG feed ramp, ejection door and forward assist). Also isn't this usually considered part of the upper? Sorry for my lack of knowledge as I am just getting introduced into the AR world. I will definitely have a lot of questions!