[lurkingknight]

CA gear axles are made of cheese. Every set I've had in a stock gun, they didn't last long, an axle would bend and the gears would bind maybe once every few cycles. Changing one gear and still seeing the issue doesn't do you any good if 2 gears have bent axles, which is possible, once the gearbox binds and stops mid cycle you can bend the next weakest point.

swapping them into another gearbox is just hiding the issue of bent axles. The axle spacing from one gearbox to the next is not guaranteed to be the same. you're talking a fraction of a mm here and a fraction there will cause them to bind.

The other possibility is that a gear face is out of round. It could be more elliptical than round. I've seen gears have faces that also wobble on the spin axis, meaning the axle is not perpendicular with the gear faces.