Had a bottle of iso. alcohol on the bench that I tried on a cotton tip swab to clean around the corners of the bolt, etc.  It does a super job of getting metal squeaky clean, but does it do any harm if I don't put on an anti-corrosive afterwards?

I would be careful, most solutions you buy in the store are a solution mixed with water.

Try and get the 91% or higher concentration.The alcohol will not hurt the metal at all.But it will strip all the oil off the metal so it needs to be oiled immediately.Alcohol is also hygroscopic and condenses water.So again dry the metal immediately and spray a little clp or whatever on there...good to go..Ive used alcohol to remove solvents from my bores for years and never an issue.
Raymond

So many excellent gun cleaners around and still people are trying to find the exotic. Yes, most isopropyl that you can buy is 30% or at best 9% water. I can get 99% at work and still don't use
it to clean my guns, because, like Blankwaffe said, it's hygroscopic (attracts water, even out of the humidity in the air). It doesn't touch carbon or most solid residue, just degreases, almost as good as
real gun cleaner. Your gun, your risk........

Quoted: So many excellent gun cleaners around and still people are trying to find the exotic. Yes, most isopropyl that you can buy is 30% or at best 9% water. I can get 99% at work and still don't use it to clean my guns, because, like Blankwaffe said, it's hygroscopic (attracts water, even out of the humidity in the air). It doesn't touch carbon or most solid residue, just degreases, almost as good as real gun cleaner. Your gun, your risk........

Thats the key to using the alcohol...surface prep for lubes...as the alcohol leaves little if any organic solvent on the surfaces.Its not so much for actual cleaning.Alcohol removes all traces of lubes and petroleum based solvents as well as ammonium salts.Thats why those of us that use lubricants like mil-comm that require a perfectly clean surface on first applications or need petroleum solvents removed from surfaces etc. use the alcohol...which is a recommended step from the folks at mil-comm.
Mil-comm also uses alcohol as a thinner in the TW-25B EP so that it can be used as a aerosol spray.
As long as the surface is dried immediately and the lubricant applied there are no problems.If the alcohol is applied and allowed to remain on the surface...air dry...corrosion does become a concern.
Raymond