I want to swap a barrel from a Sako action to a like Sako action. There are no sights or lettering that needs to line up. How much tolerance is there in how tight the barrel is installed? That is, can barrel tightening tolerance be used to make sure headspace is correct? I hope this is clear and not an uninformed dumb question.

NO. Once it is tight, making it tighter won't change headspace much; do the math and you will see. Sakos are 16 TPI, so one turn moves the barrel .0625 inches. Half a turn, .031, 1/4 turn, .015, 1/8th turn, .0078; etc. So, if you can move the barrel X amount, and keep it tight, you can alter the headspace. But once tight enough, it won't move much more. Math.
Having answered your question, here is elucidation; the headspace might or might not be ok. Most modern bolt actions are quite uniform in tolerances and barrels can often be swapped. Just check after you do it and you will know.
Not a dumb question, although contrary to the old saying, there are such things.

Thanks, that's what I suspected. You are always helpful.

quote:

There are no sights or lettering that needs to line up.

So, this is not a factory Sako barrel? In that case, regardless of how consistent in dimension the Sako actions may be, the headspace largely depends on how it was set in the first place by the person who originally chambered and installed it.

Nonetheless, the position of the bolt face and receiver face did not change and a barrel will fit two identical actions, indentically. Again, assuming the actions are of uniform dimensions, which Sakos, tend to be. Unless someone did....
Taking about a "safe" fit; not necessarily an optimum one. Try it and see; nothing to lose.