Actually after 25 years of Colorado Division of Wildlife trying to sell as many possible elk tags as they can and putting a ton of pressure on elk in Over the Counter units. The main rut in a lot of area's in Colorado has moved back from the middle of September to the first two weeks of October. Which starts 1st Rifle season and part of 2nd season in which the elk are in full rut. It has become easier to actually get a bull elk to step out of cover using a call during rifle season than it is during archery season in multiple heavy pressured units. Only once in the last 15 years has the elk rut started the 2nd and 3rd week of September in the southern units that I hunt. Main reason I believe for that was a cool and heavy wet month during that time. The cow elk dictate when the rut is and they have changed habits to start the rut during the 2 1/2 weeks between the end of archery season and the beginning of rifle season. At least that's what's happening in my neck of the woods.