I would also look at the xc. I have three of them, all on short actions. One each 7, 7.5, and 8 twist. All longer throats
Shoot bergers out of all of them and all will shoot 1/2 moa at distance. I shoot these out to 1K
115 Vlds out of the 7 T at 2960 fps
105 vld out of the 7.5 T at 3070 fps
105 vld out of the 8 T at 3150 fps
Every thing Ive killed with these have been one shot kills ...mule deer, whitetail and a 400 lb black bear at 150yds. Bear dropped and didn,t even twitch.
I could shoot 115s out of all of them but ended with a bunch of 105s and really like how they perform
As I said, I haven't had that issue, and I own a few belted cartridges and have been loading them for nearly 5 decades.
I even have one of Larry Willis' belted magnum collet resizing dies for those case bulging issues, but I have yet to use it.
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Same here, I had Willis die for a decade and never used it through half a dozen 7 mags, custom, and factory.
Lots of NONSENSE keeps getting repeated on the net about belted magnums. If a Non Truth is repeated often enough, then it is accepted as truth.
I would have the OP's chamber inspected by someone that has a bore scope. as it looks to have a scratch in the chamber.
On many chambers, if you only bump the shoulder back .002, you may not reduce the dia in front of the web enough to chamber the round when the case needs full-length sizing. Often you have to bump back the shoulder quite a ways so the case is actually full-length sized. When you have no choice you will get a bit of case stretch where the case may have to be discarded after 8 firings or so.
I started reloading the 7 mag and 300 Win mag in 1978 and never had a problem with belts in Rem 700s, Savage, Browning, and customs. Guys that are NOT advanced reloaders that have problems with a belted magnum, always blame the belt when it is their lack of knowledge that is really the problem...production dies and factory Chambers. Small base sizers per caliber often solve a lot of problems as mis matches between Factory chambers and production dies vary greatly.
The problem in the OPs chamber looks like the reamer picked up a chip that scored the chamber, and with a small mini mag flashlight with the bolt open, if you spin the rifle around on the muzzle, look in the chamber, you may actually see the imperfection. I am assuming that the scored section on the brass happens on every case in the same place, no matter what brand of brass you use.
If you have a headspace problem, often a ring will start manifesting itself partially around the circumference of the case. Some think that a "case stretch" ring will go all the way around but that is not the case many times. Then the case will separate on subsequent firings. You will extract a case head, insert a pistol cleaning brush into the part that is stuck in the chamber, and the case will come out with no effort exerted.
You should quickly and with little effort be able to determine if the chamber is scored with the small flashlight.