Thanks!! I'm shooting at a range in the middle of a state park, with hiking and biking trails all around. In addition, the park is surrounded by neighborhoods. So, they have to be extra careful, and make sure nothing is going outside of the designated areas. It was weird, I've been a member there for several years. I had been shooting that black powder shotgun for about a year with no issues, and then one day, the range officers freaked out, and were accusing me of shooting Buck shot or slugs. Black powder sounds different, and its low register carries the sound. It got to be that every time I would bring it, I would be stopped and interrogated 3 to 4 times. They would re-check all my ammo multiple times, and interrogate me on how I can re-load my own ammunition? (which is just bizarre.) They were always confused by the solid brass shot shells. A couple of times they made me stop until they got a manager to drive down, look at it, and inspect my ammo. Then, I was questioned on how could they know if I was lying, and labeled them as birdshot shot, but really put slugs in them. I got into a yelling match a couple times when they accused me of lying. The RSO's on the trap side all now know me, and know I shoot black powder regularly, so its gotten a lot better.
Regarding the plastic, I've heard enough anecdotes about melted plastic, and I've seen photos posted of people cleaning bits of melted plastic out of a pitted barrel. I think if its a clean polished barrel, anything that melts will scrub right out. If its pitted, then the plastic has a place to mechanically bond. Its not worth it to me to run plastic in it.