What problems will I have if I buy a fully assembled Lower and fully assembled Upper, both from RRA, and pin them together?  I know that I shouldn’t have any problem with reliability, but I have searched and read several posts suggesting that noob’s should always buy a full factory rifle.  However, buying the parts above will save me $300 compared to my local dealer’s price (yes he sells at near full retail and won’t negotiate) and about $125 or so versus an online dealer.  Now I know what you’re thinking…if it’s only $125, why take the risk?  Well, I agree if there IS risk.  However, if there’s essentially no risk to pinning them together, $125 is $125.  I’m not building a Franken-rifle here.  Just pinning them together.  Will I have any problems?

Pin and go   No problems.

Edit: 125.00 is alot of ammo

look at it like this - do you ever plan on EVER cleaning your rifle?  if the answer is yes, then you'll be safe pinning it together for the first time the parts have seen one another...  you'll have it pulled into two pieces the first time you clean it and every time after that so there is no issue here.

the ar isn't a toy, but it IS a relatively simple unit.  you pinning the two receivers together vs. someone else for $125 is not even a question in my feeble mind...  

do it.