Generally speaking, the fit of the SKS piston in the gas tube is fairly sloppy, at least for the Chinese version of the gun, so in my opinion it's fine to shoot it with a lightly oiled gas tube/piston. I keep mine oiled, and I shoot it that way, because it's a lot easier to clean afterwards. Mind you, I'm only shooting 20-50 rounds or so before I swab out the gas system and re-oil it. The downside is there will be a lot more oil spray in the air (and in your face) for the first few rounds, so keep this to a minimum by just using a light film...