Just wondering......where do all these go? I see 500 uppers on the EE boards, but none of them have B/C/CH's. So are they all sitting around with the socks that get lost in the dryer or what? Is there a giant military beast that feeds on B/C/CH's? Seriously, why not sell them with the upper?

i've wondered that too.  if you're not supposed to switch them out (bolts) than how come they're not complete?  maybe to sell cheaper?  

Dunno 'bout anybody else, but when I sold off my SP1 upper some time back, it was with the intention of mounting a forward assist type on my rifle, so why should I sell off the bolt/carrier, handle when I'd just have to pay more than I could get for them to replace them?

I suspect that the vast majority of the time, the same situation exists for others who get rid of uppers.  They're not selling the whole rifle, so obviously they have plans to build something on the lower, and will need the bolt/carrier and handle.

By the way, if you have a Colt or military contract bolt assy, 99.9% of the time it'll headspace properly with any properly built upper assy.  Bought 4 well used Colt military contract bolt assys last year for $15 apiece, complete. Headspaced them in four different uppers. Three were well under max, and the fourth, while it closed on Max, did not close on the Field guage.  That one was so old, it still had the white insert in the extractor spring; indicating that it was at least 35 years old[:D].

Now I specify Colt or Mil surp, simply because I know they're made right.  I have no data on aftermarkt stuff; and while I'm sure that anything from one of the major aftermarket folks is OK, I'd rather go with what I know is good stuff.  Besides, the price on those mil surp pieces was too good to pass up[:D]