Speer makes
plastic training rounds that are powered by just a primer and use very durable and reusable cylindrical projectiles. The only tool you need to use them is a nail to poke out the fired primers.
When I bought some in 1974, the prevailing wisdom said these were great for practice at home and the projectiles would be stopped by a heavy blanket. There was no mention of using the carpet scraps that are currently recommended.
Sooo - I draped a very heavy blanket over an exercise bar I had put at the top of the doorway to the kitchen in my tiny NYC studio apartment. I then proceeded to load my revolver and fired with the expectation that there would be a little "pop", the blanket would pucker backwards as it decelerated the round, and the expended round would drop neatly into the cardboard box I had placed underneath to receive it.
What actually happened was: there was a really loud "BANG" in that little apartment. The projectile's energy was not observably dissipated by the blanket. In fact, the blanket didn't even move and a perfectly round hole appeared at the point of aim. The round continued at close to initial velocity on about 6 feet until it encountered the refrigerator. The outer skin of this appliance did deform (permanently) and absorb some but not all of the projectile's energy. It also redirected the the round in a direction that allowed it to make contact with multiple other surfaces in that tiny room until it came to rest spinning on the floor.
The wife was not pleased.
That being said, for OUTDOOR use in revolvers, those plastic rounds are really neat, dirt cheap to shoot, and a lot of fun when used in the proper environment. They are also definitely not toys and should be treated like any other live ammunition.