Gregory,
As KN said, you can use one bolt and carrier in two different uppers.
However, it's a LOT safer to get a new bolt for your second upper and just use the one bolt carrier.
The reason is that after a while, a bolt will sort of "wear" into the barrel it's usually fired in. If you then put it into a different barrel you could end up with headspace and/or other problems. Be safe, bolts aren't expensive.