Yeah, I've had mixed results at the Cherry Creek range.
Was there last weekend sighting in a new Model Seven, and one range master, upon seeing my AR, immediately gave me a lesson in the proper way to employ the carpet-covered brass blockers. He also asked that I sit far forward on the bench so that my muzzle break would be outside the window. Friendly, but a little condescending.
I worked on the new scope, and decided to shoot the AR while the barrel of the M7 cooled. Not very fond of the diamond-shaped targets with the irons, and asked a different range master if I could shoot a different target with a circular bullseye. Yes, the fee pays for only one rifle target, but this had been acceptable in the past. The second range master insisted that I shoot the AR at 50 yards. Not exactly what I was looking for after making the drive from Boulder.
I think that if you go to the range with an (iron sight only) AR during the typical pre-hunting season sight-in days, you will have little chance to shoot at the 100 line on a busy day. Now's not that time, so this ought not be an issue.
At other times, there has been no problem for me, so I guess that your chances of shooting at the 100 yard line depend on the amount of traffic and the individual range guy. I know, this is a little irritating. In the worst case, set up at 50, demonstrate that you can keep the shots in the middle, and then ask to move. It's your $.
Maybe we'll get some precipitation tomorrow, and the guys will let you sit beneath the roof.