Straight Line/mark Inside Barrel

In firearms, the gas system is responsible for redirecting a portion of the high-pressure gases produced by the firing of a cartridge, to operate the firearm's action. This can be done through a gas port on the barrel, which is typically located near the chamber, or through a gas block mounted on the barrel.

One potential cause of the mark you have described could be excessive wear on the gas port or gas block, which could be caused by a build-up of carbon and debris, or by a lack of regular cleaning and maintenance. This wear can lead to leakage of gas, which can then cause erosion and pitting on the inside of the barrel, resulting in the mark you have described.

Another possible cause of the mark could be that the gas system is not properly adjusted, this can cause the firearm to malfunction or not to cycle properly, leading to high pressure on the barrel and cause the mark you have described.

It's important to note that the mark you have described could also be caused by other factors such as improper usage or improper ammunition, if the ammunition is not suitable for the firearm it can cause high pressure and damage to the barrel.

It is important to consult a qualified gunsmith or the manufacturer for proper diagnosis and repair. It is also important to note that if the mark is due to excessive wear or damage to the gas system, this can result in significant loss of accuracy and performance and can also be dangerous, as it can cause the firearm to malfunction, potentially leading to injury or damage to the firearm.

It's always recommended to follow the manufacturer's guidelines for proper usage, storage and maintenance of firearms, this will help to ensure safety and longevity of the firearm.