I will soon be replacing my Colt HBAR 20" barrel and was wondering if I should also get a new bolt. I've fired approximately 12,000 rounds but the bolt looks okay to me. Can I get away with just a new barrel?

If it's a Colt bolt assembly, you probably can reuse it.  Given the number of rounds you've used it for, I would check the headspace, tho.

All my ARs have GI surplus Colt bolts in them, probobly Viet Nam War issue. Despite their age and the use I assume they got before they were stripped out, 4 of the 5 checked out under max, and the fifth, which was clearly the oldest, wouldn't close on the field guage, so it too was usable.

Colt's bolts and carriers are truly built to last forever, and I'd rather have those used pieces in my rifles than any new aftermarket job.[:D]

Hard to say, I've swapped bolt assemblies from one AR to another, but I know how they've been maintained and lubed, also none of mine had over 5k rounds.  If you don't have a head spacing gauge, may be the best thing to do is to buy a new stripped bolt (around $25) and transfer the firing pin, ejector & extractor over along with new gas rings.  Cheap insurance in my book.

I think I might continue using my colt bolt then after checking headspace. If I do have to buy another bolt I was considering a Bushmaster bolt. I guess I should have mentioned that the barrel is going to be a Bushmaster. I was under the impression that Bushmaster, Armalite and Colt were equal in terms of quality and durability. Am I wrong in thinking this?