Do I have a chamber problem?

[303Guy]

That kind of splitting or cracking looks like age embrittled brass. I've had cases that split before firing.

Five rounds in a white box (reloaded?), came with the rifle.

the white box ammo had two long cracks at the neck area.

Reloading without annealing or very old cartridges. Lack of annealing usually splits the cases from the mouth down but not always. I've only seen the shoulders split from age embrittlement.

Those cases have some serious expansion above the web. The Remington cases look the same. Are those nickel plated or cupronickle? Those do not look like reloads - those cases are factory fresh.

The chamber does seem to be generous - that's a lot of web expansion and it's visible on the Remington cases too (can't see how much on them). Only measurements will say for sure. You can measure the base of the case and compare that to a drawing. They should be around 0.4554 inch just below the expansion ring (0.2 inch from the rim). The diameter of the chamber at the expansion ring can be found easily and compared to those cases.