Any calls are only as good as the caller to produce the right sound. The bugle should only be used to locate a bull then move into his space or safty zone and use the cow call to entice him in closer with limited calling.
I have to agree that bugle can run a bull off in areas that are hunted more and even a cow call can do that because in many places elk are becoming call wise and has turned into a spot and stalk or cutting them off to and from there feeding area. If you are trying to vidio them this time of year a cow call will be your only hope and probly only to stop them and you would have better luck during the rut assuming they rut arround the same time as up here in September into the first part of October. See if you can get a vidio on call ing elk like Wayne Carltons or the Quaker Boys vidio on calling elk and that will give you a better idea on hw to do it.