Interesting observation .. however I think you may be operating under a misnomer .. machine gunning is not the most common form of LR BR in Australia. It is certainly the method in the USA but here its a different story, as many blind shooters pick there way through a condition as machine gun, in fact I would say picking is more common than machine gunning ... so the time issue really does not come into it.surely one of the reasons that the spotted method is less successful than blind in BR is that you have to wait for the target to be pulled down, spotted, then raised.
At shoots I attend it is more often the blind shooters that are firing their last shot in the last 30 seconds, while the spotted shooters have long finished and started cleaning.
I (and it is only MHO) believe that the primary reasons for the success of blind shooters lies in the lack of feed back.
You really have to trust your equipment and wind reading skills and I believe that blind shooters concentrate or focus more due to the lack of feedback.
I also believe that blind shooters are advantaged by no feedback in that they dont receive contradictory feedback. Sometimes ignornace is bliss.
The clear mind with simple thoughts of technique and wind condition has less to distract it from the task at hand .. ie
"Shit where did that come from"
For group shooting the position is less important than maintaining the group. For F Class the score is more important and as such different rules apply.
Why don't you drag yourself to Canberra for a 1000yd shoot and we can compare notes they shoot on a Sunday and finish about 130 -2pm so you could shoot Sat arvo with the Canberra club and then shoot the 1000yd Sunday.
After all everytime you shoot you learn something new.
cheers
Rinso