i was looking at the benefits at the m16 bolt carriers, and decided to look them up on gun broker or in the EE. then i remembered, isn't it bad to get a used bolt? because what i remember reading was that you shouldn't switch carriers between different uppers? i didnt know if that info was just a theory or whatnot. thanks. (sidenote, i just got my membership! yes! cant you change the avatar?)

You can swap the carrier from rifle to rifle, but I wouldnt swap a bolt from rifle to rifle.

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Well it's considered by most people to be bad karma if you switch the bolt and carrier.  Some companies even offer "matched" bolt/carrier and barrel packages.  Personally I think its bull puckey because if it's built MIL-SPEC then it should be interchangable and if it osnt build MIL-SPEC then why in the hell are you buying it in the first place?  Anyway thats my .02.  But I wouldn't buy a used carrier because different recievers can have different inside diameters by hundredths of a milimeter but that tends to be enough to cause problems in rare cases.

EDIT: oh and benefits are weight.

thanks guys, if i end up deciding to get one i might as just put in the extra bucks and get a new one. thanks!

I wouldn't make a habbit of switching bolts between rifles as the wear patterns are different between each rifle and can excesivly wear the bolt..

but..

If the bolt headspaces okay to the barrel, you are good to go. I don't put to much stock in the "matched bolt" bit when it comes to ARs.. just needs to have good headspace.