Fouling is the enemy.
I recently received a customers barrel for evaluation. Upon inspection of the bore with a bore scope, I discovered severe fouling. As many of you likely have not seen this kind of fouling, I wanted to use it as a learning moment. The barrel shown here is a 26 nosler, with a reported 400rnds through it.
Here you see the very front of the chamber. Carbon ring, heavy heavy carbon ring. Wicked carbon and copper fouling.
As you get further down the barrel, you can actually start seeing rifling.
Here it is after cleaning. You can see the carbon ring is gone, and the front of the chamber mouth is defined.
Even after cleaning, you can see the extreme pitting and erosion that the area just in front of the chamber exhibits.
Farther down the barrel in front of the severe erosion, fire cracking is evident.
I bet the fire cracking coincides with a reduction in barrel diameter and tube wall thickness.
Less material to resist pressure deformation of the bore.
Jeez toasted barrel after 400 rounds.
I assume with the fire cracking it's toast or dang near toast.
I wouldn't call the barrel "done" yet... but it is certainly on its way out. Gator skin typically needs to get way worse than that before the barrel truly runs off.