Thinking of getting a gas powered airsoft for practice in my house. The one i'm looking at getting is powered by green gas. I've heard green gas is the same thing as propane. These guns shoot at around 300fps. Are they safe to use in the house? Will it put dents in the walls or other objects? How about the smell from the gas, is it a strong odor that will last for a while? I've never handled one as is obvious from the questions.