I once had a squib on a .38 special tracer load. I had an old box of them and we were playing with them at night. It sure gives you a real picture of the arc a .38 makes in flight.
The squib tracer was interesting to say the least. It got real hot in the barrel, and lodged itself in pretty good. I had a heck of a time getting it knocked out. In the end, there was no real damage to the barrel.