Most epoxy breaks down at temperatures under 300 degrees F.
Even the best high temperature epoxies break down at around 600 degrees F. These temps are considerably less than hot powder gasses, and most pitting tends to occur back where powder gasses are hottest. Even though the duration of extremely high temp is very short, I'm quite certain the combination of temperature and pressure would quickly erode your thin epoxy veneer.
There's a reason gun makers use steel to make gun barrels. You are expecting epoxy to do something it was never intended or designed to do.
