Which of the following is a possible outcome of fire lapping?

Fire lapping involves shooting specially coated bullets through a rifle's barrel to subtly polish the bore and improve its internal surface. This process can indeed lead to changes in bore dimensions, particularly at the chamber end, where fouling and imperfections can accumulate. By using fire-lapping bullets, the interaction between the bullet and the barrel can wear away rough spots and tight areas, potentially increasing the bore diameter at the chamber end. This outcome can help achieve a better fit and enhance performance, especially if the chamber has imperfections that may impede accuracy.

The other options, while related to the performance of firearms, do not accurately describe the outcomes associated with fire lapping. Improving accuracy without modifications involves other tools or practices but isn't a direct result of fire lapping. Similarly, while fire lapping can marginally affect velocity due to improved sealing in the barrel, it does not significantly increase bullet velocity. Finally, the process focuses on internal smoothing rather than perfectly finishing the exterior of the firearm. Thus, option B correctly identifies a plausible and realistic outcome of the fire-lapping process.