Must be several factors (direction/intensities of force) involved in this.
How strong is the slide stop shaft?
How hard does the barrel lug strike the slide stop shaft when the slide slams forward to chamber the next round and lock the barel up in the slide?
How hard does the barrel lug strike the slide stop shaft when the slide pulls it backwards and ejects the empty?
How much stress is on the slide stop shaft when the barrel is behind held fully up and locked into the slide?
What are the effects of the parts pushing/pulling/beating together when one or more of them are "in spec." but still off "perfect" enough and in a direction that results in more force being required to make the barrel/slide stop shaft/slide work together to function?
And some more I haven't thought of, no doubt.
It's why some slide stops last longer than others.
