Good catch, Sniper, incredible that S&W did this. They're lucky most people never remove the FSB as there would be a lot more unhappy customers. A while back I remember reading a post where someone was banging away trying to remove a S&W sight base with no luck. No wonder!
Guess it's always wise when removing taper pins to make sure which side is larger.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek