It is confusing to me with all the different upper and lower combinations available for the AR type firearm.In my case,I have an Armalite AR-10,a S&W AR-15,and a Bushmaster AR-15.I see a lot of uppers and lowers I would be interested in as upgrades,(Larue,Noveske etc..)but I am not sure if they will interchange with my stock set ups.Your in-put will be appreciated,Thanks in advance.