I have a 375 H&H O/U double rifle,the rifle shoots real good,very accurate,has been worked on,the only problem still unresolved is the top barrel,the spent case from the top chamber shows a ring or call it a stretch mark right above the belt,,if I reload this case? the head separates just ahead of the belt,the cases are pretty cheap & I could just shoot it as is,but I would like to clear up this problem if I can,what do you think can be done if anything?

Does a new case or round fall into the chamber below the level of the barrel face? Probably; classic case of excessive headspace, which in that case is the belt front to breech face distance. I would do like you do when making a wildcat case; form a little false shoulder for the brass to seat on then do not resize it too much after that. Treat it like a rimless case.
It happen a lot with the belted mag family as the chamber specs are quite liberal, for some unknown reason. Something like .018 is allowed between min brass and max chambers. I am too tired to look it up again but it is huge.
Now, if your rifle is loose enough to be hinging open upon firing, then you have another problem to fix.

Typical case of excess head space, most belted magnums are a little sloppy fit as factory rounds but if not reloaded, not a problem. Easy to fix when reloading by partial resizing so as to seat on the neck. Problem with an O/U or SXS is that if only one chamber is showing excess headspace then you will likely need to have different sized cases specific to each chamber/barrel. Doubles do not take too kindly to having tight cartridges to close on so if cases are partially resized to suit the 'loose' chamber odds on they will be too tight in the 'tight' chamber and closing the gun will be difficult.
Oh the sweet joys of bolt actions

Normally what happens in this case, is that the cartridge is driven forward by the firing pin and the soft, light forward section of the case expands and grips the chamber walls with pressure buildup. As the case pressures up more it drives the base rearward to take up the space between the case head and the breach which basically tears the head off of the case.

As a rule, the simple fix is to install a header ring. The belt area of the chamber is cut forward about .050 inch and a steel ring whose ID is a couple thousandths of an inch smaller in diameter than the original ID of the chamber is soft soldered in. A chamber reamer is then run in to match the headspace measurement of the good barrel and the ring and chamber are polished and blended together with wet & dry sand paper. After being repaired the base of the cartridge is held back properly and the forward section simply expands normally to fill the gap at the front. Just as it would if you were fire forming cartridges.

I'll second Eagle. I experienced early incipient separation indication (internal groove just above case head) in my FN CCS25 o/u 9,3x74R after 1-2 firings. The problem was solved by partial sizing and I now reload 3-4 times before dumping the brass (out of precaution, no separation signs). However, the partial sizing technique differs a bit between double and mono-barrelled rifles. With the latter, you partial size until your bolt closes with a little feel (you have just attained about 0 headspace). High class double rifles being mostly handmade, they quite often present chambers that are not rigorously identical. Therefore, a compromise has to be found in order to allow correct chambering in both barrels. I did, testing the processed cased in both chambers and I stopping sizing when I reached the point of compromise (= a -very- light kiss on the shoulder) where the rifle closed easily* with the partial sized cases in one or the other chamber or both.

*Double rifles (hinged) don't have the rigidity of a bolt rifle. To avoid stressing the hinge, it is best to tolerate a little headspace (case life won't last 10 reloads but you won't strain your double).