Usually new brass means new barrel. You can try to see if you can fit your old brass, just don’t jam it. And I’d also take a hand full of pieces and fire them a few times to see if you end up with clickers.
I’ll use the same brass if barrel is chambered off the same reamer.
You can have issues with the case head area of the brass being different enough that it causes issues in a different chamber, sometimes not even chamber.
Not all old brass will fit all chambers - usually the problem is the diameter near the case head is too large since this area doesn’t get squeezed down completely with normal full length dies. Small base dies can usually fix the problem, but simply buying new brass is cheaper than a die that rarely gets used.
One time years ago I was trying to use some free brass picked up at the range and they wouldn’t fit my chamber and the diameter around the web of the case wasn’t too large for my chamber. Something about the angle of the shoulder wouldn’t get pushed back completely with my dies. Using a thin case holder would have allowed the shoulder to be pushed back more, but at the time I just gave them to a friend and they seemed to work ok in his rifle.
I say go for it and if a sized case fits you’re money ahead.