The "tab" is actually a keeper.
It's there to hold the wedge in the left side of the barrel when the wdege is pushed free of the cylinder arbor. The little screw that sits above the wedge (in the tab groove) is the stop for the tab. Ya see that wedge ain't like a rifle key, it's actually wedge shaped.
If your pushing the wedge all the way through so the tab is outside the wedge slot on the right, you could have it too far in. The tab doesn't have to, go through till the tab catches out side the slot.
This whole set up is how you adjust the gap between the cylinder and the forcing cone of the barrel and that gap is an individuals preferance, something that every Colt has unique to it's self and the owner. It might work well for you now, but a fired dirty cylinder might not turn well if that gap is too tight.
Guy's will file on the wedge and/or the slot in the arbor to get it like they want. A Scary thing for a new owner to do, I found some advice someplace I can't remember where that worked well, one half of a common wood/spring clothes pin give your hand something big enough to hang onto and fit's nicely against the wedge.
Steal one of the wifes clothes pins, pull the spring and you have two wedge tools for the box, :wink:
