I have just ordered a 20" 1/9 barrel to replace an old 1/12 SS barrel. The new barrel comes with everything accept the handguards and gas tube, which I plan to replace.

My question is: Since I am using the old upper receiver, should I replace the complete bolt/carrier assembly, or can I just replace the bolt and use the old carrier.

I just don't feel comfortable using the old bolt (with many rounds shot), but the carrier has "worn in" to the receiver, is smooth as silk and won't be affected by the barrel replacement.

You can use the old carrier.