Hearing that you were using the factory crimp die had me fairly convinced that was the cause of your chambering problem, which is why I suggested running fired cases through your rifle before doing any sizing or other operations. Hearing that all of your fired cases chambered just fine, and seeing the photo of the loaded cartridge makes me 100% convinced.
That is wayyyy too much crimp, and as I said, none is really necessary in a 6 mm Rem. Even when I do use a crimp on cartridges such as .357 mag, .44 mag, .45-70, etc., I use a much lighter crimp to hold the bullet in place because excessive crimping works the case neck far too much, leading to premature neck splitting and short case life. And as you have seen, once that crimp has a death grip on the bullet cannelure before seating is 100% complete, the only thing that will move is the neck and shoulder of your brass... leading to buckling or bulging. You don't need to smoke the cases to see it in your example. A firm crimp supposedly helps with consistent ignition with some pistol powders, but again, too much crimp is working the brass too much.
If you have a few loaded shells that won't chamber at all, you may be able to carefully roll them between two smooth pieces of steel to work the bulged area down just enough to permit chambering. They will then fire-form to your chamber, and will then fit perfectly. No need at all for full length resizing if the cartridges will be used in the same rifle. Neck size only for best accuracy and long case life.
