LOL! Finally......an expert.
Leave it to Dave to introduce a new term to an already complicated topic and muddy the waters even more.
Terms already thrown around and misunderstood by some are......."spring holder" "kick" and "spacer."
Now we have "choil."
Oh joyl. Now we toil. We have to consider the Dave sense of humor here. There's a chance that he may actually enjoy confusing the newbies, as he calls them.
I think it's the KICK that has the task of stopping that precious and delicate blade edge at the tip from hitting that "spring holder" or "spacer" as some choose to call it. The choil, being more of a divot or notch than a projection--would not be likely to stop anything.
But who knows? As with all things Buck there can be many answers to the never-ending questions.
Anyhow, here's info that may help all of us that are not elderly enough to own 500 110s.
http://www.blademag.com/blog/can-define-knife-choil
"""Be that as it may, the chief purpose of the knife choil, as noted by the definitions of both Russell and Collins, is to allow the full length of the cutting edge to be properly sharpened. In other words, it is simply a small notch between where the cutting edge ends and the ricasso or the blade tang begins that indicates where you should stop when sharpening the blade with a stone, diamond-coated abrasive or what have you."""