I am considering building a rifle using a Winchester 70 Classic SS 300 Weatherby magnum action and instead of buying a custom barrel I am considering using a factory barrel from a Winchester 70 Classic SS 375 H&H, the owner said he removed the barrel from his action due to a case head separation. I would like to find out what I should be looking for when I inspect the barrel or should I have a gunsmith inspect it for me ?
From my reading I found out that one of the main reasons for this type of problem is due to excessive headspace, basically the factory's chamber reamer may have been a little worn out when the rifle was manufactured. I also read that a barrel could be reused but it would need to be set back and rechambered to tighten the tolerances. Another reason I read about for case head separation could have been due to the lugs and seats being worn or issues with reloading the ammo. I am still making my inquiries, so the exact problem is yet to be determined. My question; Is the barrel still safe to use and does anyone have any experience with reusing a barrel like this before? Thanks

Years (and years) ago, bought a used pre-war M70 Supergrade in 300 H&H. Fired 3 rounds of factory ammo and all three had casehead separation. Took it back to the gunstore where it was purchased and they verified excessive headspace. Due to an upcoming hunt, couldn't wait for a fix so traded it for another rifle. The store cut the barrel shank back, rethreaded and rechambered for .300 WM. Proved to be an outstanding shooter with no problems. Didn't want it after altering the original rifle, but someone ended up with a good one.

Any gunsmith who is familiar with barrel work can measure up the receiver and barrel, and thereby determine whether the headspace will work out OK. Rebarreling a gun is not like plumbing work in the bathroom. It has to be done right or it can be dangerous. The single most common reason for case separation is a reloader who doesn't know what he is doing. The barrel in question may be in that category. If all else fails, it should be possible to set the barrel back a small amount and clean up the chamber with a reamer.

Thanks for providing some feedback, all your responses have helped me to better understand what case head separation actually involves and what may have been the root cause. Personally I have never had this happen to any of my cartridges since all I have shot to date are factory loads and I do not reload.
A respondent from another forum addressed an earlier comment I made regarding the worn chamber reamer and excessive head space problem, he stated a worn chamber reamer would result in insufficient headspace, not excessive. This sounds logical and correct.
The primary reason I wanted to use an original Winchester barrel is to preserve the identity of the rifle as a Winchester 70 Classic SS, additionally I thought I would be able to save a little time and money on the turn around. I am starting to see that there may be some precision barrel work involved in getting the correct head space and additionally to insure that the barrel lines up correctly for proper sight and extractor slot alignment.
My main concern with using this barrel was safety, since I would be the one carrying the rifle in the field. Since most respondents agree that the barrel and chamber would not be damaged by a case head separation then I am convinced that the barrel will be safe to re-use. The owner has offered to have a gunsmith check it out before selling it to me, I will decide after I get the gunsmith’s report.
Nukalpiaq

Here is an excerpt from the owner's response to my inquiry regarding the cause of the case head separation.

Quote: I'm convinced it was caused from weak/over-annealed brass. The load was a starting load for the bullet and powder combination...using rounds that I loaded for a trip a couple years prior. I pulled all the bullets in that batch and verified powder type and weight...all the gas and pressure came back through the action...There have been less than 100 rounds down this barrel.

You might just have your present bbl rebore to .375 and go with .378 weatherby. Or rechamber the available H&H bbl.