Couple things, which relate to your question:
Pay attention to where your rifle is throwing brass. You aren't in a war zone like TTR, you are at a range punching holes in paper. Take advantage of that to learn your rifle. You want the brass to be at 3 O'clock to 430 and a consistent distance away. My AR tosses it 10' tops my MINI 14 throws brass into another zipcode. Different ammo will throw differently. I'm getting Federal Lake City @ $.36 a round right now, so that is all I shoot out of the AR, and shoot Tula out of the MINI. When the same ammo starts coming out of the gun differently something is up, maybe not wrong, just up.
You can use motor oil no problems, in fact I keep a stick of lithium grease in my range bag incase I have issues (more on this later) to lube my rails.
You, again, are at a range and not in a war zone, the rifle doesn't have to be spit shined every time you use it. I clean after every trip, unless I shoot less than 100 out of it, but I don't get it immaculate. Clean your chamber good and the barrel for sure. Give the BCG some love and you're all set just wiping down the rest of the shit.
I use 3 things to clean. Straight acetone to clean. Then I'll use a cheap CLP on a second bore snake to keep the barrel from rusting, and Frog Lube on the rest of the internals. Shit evaporates quick, so move fast, but it breaks up any gunk the world has ever seen. So if you don't wipe fast the carbon build up just becomes thicker sludge that is harder to clean lol.
Some people HATE frog lube. Their marketing is bullshit, and it tends to gum up in the cold. I just work my action a dozen or so times and it seems fine so far, but I also don't lube the shit out of my rifle. My bold and pins themselves are "wet" and the RAILS on the carrier are "wet" but for the most part my bolt is dry. Frog Lube stays where you put it, therefore you don't need a ton. Any oil or CLP that travels... You're best bet is to lube before your range trips and coat for rust prevention while it sits in the safe.
My main reason for Frog Lube is the kids. My daughter will "help daddy" clean his guns from time to time, and seeing as she is two, I don't have to worry about it getting on her hands and her eating it. (She mainly just piles up the patches and qtips in a cup over and over, lol.)
I've seen people running ARs that are basically soaked in grease and oil, and cleaned for hours after every trip. Compared, I run my shit dirty and dry, lol and it runs like a champ. I'm well over 1k rounds and haven't had a single issue, not even mag related. But I don't run bullshit ammo through the thing either. I save that for the MINI.