I've never been able to get a 45 minute burner out of an average kingy. If at that size I manage to get the mix precisley right it could hold out for a good 10 minutes maybe 15 if Im smoking it by myself. It is hard though, usually I want to get high straight away so I don't put much effort into the joint just aslong as it tokes well.

If I want a 45 minute joint I will roll a magic carpet with kingy's and add an extra kingy too the lengh, mind you this takes up so much weed you might think its better to roll a blunt, but for me I have always preffered joints.

Just keep practicing, get your ratio of baccy and weed right, and if you don't use baccy make sure your weed isn't to compressed or too loose.