I am new to these rifles, so I hope this won't be too stupid.
My question is, if I have an upper with 1 bolt and carrier, can I just buy another upper that has been headspaced and put those parts in or do I need a bolt and carrier for every upper?

Thanks in advance for taking the time to look this over.

you headspace the bolt to the chamber.



suggested you at least get each upper its own bolt.

One bolt/carrier group would likely function fine in two uppers. However, if you're switching it back and forth a lot, I suppose it can wear unevenly (based on slight differences between the uppers), and would probably wear out sooner.  After thousands of rounds, perhaps you'd run into headspace issues, but for recreational/range use, I think you'd be fine.

You don't NEED a separate bolt/carrier for each upper (although eventually you'll probably end up buying one, just for the conveience - and then of course anotehr lower - and then you'll have TWO rifles before you know it )



ETA:  Or, I am completely wrong - and you should listen to eklikwhoa's advice.  But in my personal experience, I have switched bolt/carrier groups between various rifles I own on multiple occasions, and put in replacement bolts in rifles without any issues whatsoever.