AR-15 Question on a replacement upper

[Gregory]

I have a Bushmaster Varminter flattop setup with a scope.  I was thinking of buying another upper in A2 configuration with a shorter barrel to use as a plinker and self defense house gun.
 
My question:  Can I use the bolt and charging handle from my Varminter on a new upper or do I need to buy a complete upper assembly with a new bolt and charging handle?  I don't know if the bolts are matched to a specific receiver or not.
 
Forgive my ignorance on this.

[KN]

Yes you can use your bolt and charge handle. I have a Bushmaster Shorty and a complete DPMS heavy upper that I put together and I use my bolt and handle from my shorty.   KN

[CAV Trooper]

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.

[Gregory]

Thanks guys

[Savage]

Does the bolt carrier come with the DPMS upper? If it does you can buy a new bolt for about a $100. Seems like that would be the way to go.
Savage