Shooting off early is not really a big issue, as the set environment is not particularly sexy and the performers are working, not really having sex like normal folks. The biggest challenge is usually blowing a load at all! There's a lot of work you need to do to get there, healthy lifestyle is key along with practice on your PC muscle, and training yourself to focus an the er.. task at hand, so to speak.
If you've watched enough gangbangs you will see that the guys aren't really queueing, they are usually off to the side and working on getting themselves close (sometimes they are even watching porn which I find quite funny) once they are close, they will edge until there is a free spot, and head over to do the deed. That's why the last cumshot usually has a big gap, or an edit - someone is usually having a hard time!
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