I apologize for this in advance. I'm new to them but have a handful of questions and people here seem to be helpful and to the point. I have a few, so answer what you can or what you feel like, thanks in advance. What kind of optic is this mounted on the gun, and how does it work (What do you line it up with I guess..?) And a second pic. for reference (again): What type of optics are these, and why do people mount them on different parts of their receiver or even the top side of the barrel? I've noticed people move the one above around quite a bit too. Whats the deal with the 1/9, 1/8 and 1/7 twist thing? I'd imagine that is the amount the bullet spins as it comes out, or has something to do with that. Which is better than? I'd guess 1/9 is the most common.