I used the center pin of the bat con, as you've described, take a look
here
the main waste of time during making mine was in having to file down the edges of the washer that I later pressed into the flashlight. Sure, it's an all mechanical connection, allows it to be more compact, but i spent half an hour hand-filing the edges of the 1" fender washer so it would press it. The other problem is that, because the battery is always pushing on that center pin you have to pull the battery before you loosen the atty or the pin gets popped out.
I think it's a neat trick, but limiting in some ways.
on the other hand, I think my "clickie" replacement below can help reduce size for the smaller 3*AAA flashlights.
except that in this situation you usually need to reclaim that space inside the tail-piece so the longer 18650 battery will fit