There may well be something to that, BR. And the rougher the throat, the worse the "obstruction" might be. There IS a correlation of these events to rifles with worn or dirty throats, so maybe...
The only quibble I have with your post is the word "spark" because the primer does a whale of a lot more. It's quite the small-scale explosion, in fact. The primer alone can generate over 3,000 psi and temps of over a thousand degrees.
