So Im a noob. Everyone has to start somewhere right. Simple question that has me wondering,

Can I switch the bolt and charging handle between two different uppers?

I picked up my first AR the other day. Its got a varminter barrel on it, and I got hime to throw in a carbine upper for a good deal. It didnt however come with a bolt or charging handle. He said no big deal, as I allready have one in the gun, which I would say is logical. However, as reading through the manual, it boldly says, in several places, "Do not use bolt in another gun!" Is this them just covering their asses, or is there a good reason for this? Thanks

You sure can swap bolts. Just buy a set of headspace gauges and be sure that all is OK.

The problem you run into is head space.
Your chamber is cut to a given depth.
The face of the bolt is a certain depth.  If you get a bolt that is too deep and a chamber that is to long the brass expands to much and tears and you get a boom.  Most of the time you get tear, tear tear, broken case stuck in the chamber and then boom.  But don’t rely on that.  With new guns 99.9% of the time you can swap bolts.  Most of the problem is If you have an old barrel and you put in an older bolt they may have worn so bad they are out of spec.    

I would not move the bolt from gun to gun although it can be done.  The bolt wears over time as well as the chamber and they become somewhat of a "matched pair."  Bolts are cheap.  Get one for each upper and keep them with that upper only, IMHO.
Bolt Carriers on the other hand move easily, safely, from upper to upper.  There is not a headspace issue.

Now how does that affect hot-swapping bolts if you break a lug or something? Should you headspeace-gauge your spare bolt ahead of time?

Quoted: Now how does that affect hot-swapping bolts if you break a lug or something? Should you headspeace-gauge your spare bolt ahead of time?

I just check all of my bolts (well, b/bc combos) against all of my ARs. And as said above, there can be differing wear on different bolts and lugs, so it never hurts to check once a year or so if you plan to swap.  Takes a minute or so.

I don't think you can switch the varminter bolt to another gun. I was cleaning them the other day and almost put the charging handle in my 16 inch and it wouldn't fit. The Varmint one is mated to the gun they say. I would do it on two standard weapons if you HAD too.
JR

Quoted: I don't think you can switch the varminter bolt to another gun. I was cleaning them the other day and almost put the charging handle in my 16 inch and it wouldn't fit. The Varmint one is mated to the gun they say. I would do it on two standard weapons if you HAD too. JR

The Varminters bolt is supposedly 'tuned' to the rifle, but there is nothing non-spec about it, to the best of my knowledge.