Yes, it would be great to be able to go back to the .225 in spring. So if there wasn't a nut, headspace is determined only by how far it threads into the action? If I went the nut route, are there other barrels that would be swappable or would I just order them with the right threads and thread length for the nut? I've sanded inside the stock a bit but I think it still touches when it gets hot. I would certainly go the extra mile to pillar bed and free float the action and new barrel. I don't mind the trigger at lightest pull so I can leave that as is.
with the rim cartridges like the 225 the headspace is determined by the rim so the critical dimension is between the bolt face and the chamber where the rim sits.
In any case it is a good idea to have things zeroed so the case shoulder will also zero at optimal length according to your dies this way avoiding stretching the brass during firing.
Either way w/o a barrel nut one controls this by cutting a bit form the tenon shoulder so additional machine time is required to get a proper head-space and cambering job.
For a barrel nut swap your .225 will have to be retrofitted extending the threads to allocate the barrel nut that is not a huge deal but you need to extend those threads for
whatever barrel nut you choose.
Initially I think Ruger barrels are good candidates since they share the same threads and some come with barrel nuts but personally I prefer the Winchester barrels that can
be simply threaded for the same purpose. Even an old pre 64 barrel can be retrofitted by extending the length of the tenon and threads but the modern winchester barrels
have better bores and more consistency therefore assuring more accuracy potential.
I think after you do one barrel you can get a rough blueprint and then it will be easier to find what barrels will work better w/o any or minimum machine time.
You also have the option to go with a smooth custom barrel nut but then this is a piece that will have to be machined and blued. Not a huge thing and only a one time
deal but something to consider in terms of cosmetics.
The inlet might need the removal of some wood for the nut but then it is a perfect time to do some bedding and make the entire rifle a more consistent shooter.
You also will be able to order barrels from makers with the thread length that you want. The whole idea is to have something you can swap yourself so it might be
time to invest in a couple of tools. I proposed this from the beginning because you wanted cost effectiveness but there is also the versatility factor. Most folks
who have a workbench and a vise in the basement have no problem learning this process. However if you are the type of person who is not mechanically oriented
then this is not for you. Again not advanced skills are needed just a couple of tools and some patience. If you are a reloaded most likely you are good candidate
to swap barrels w/o issues. I think there is also the fun part and sense of pride to be able to improve and enjoy the rifle your grandfather left you.