Bought a lens but the aperture seems hard to move

[Don7x17]

If the lever is sticking due to gummed up lubricants, the best way to free it is to put a drop of lighter fluid (get the kind that is namptha, not butane) at the spot the metal meets the lens body -- not much. Work the lever a bit and blot the crack with q-tips. If this is the issue, the qtip will blot up black-ish fluid. One or more such applications will take care of the problem. The namptha does not affect either metal or the older mica-like irises on older lenses, and evaporates quickly. An old camera repair guy that worked on ILEX shutters showed this to me.
I've used this sucessfully on several (very old) expensive brass lenses with iris (but no shutter).

[domaz]

Copal 3 shutters require a spacer ring and usually come equipped with one.

Copal 0 and Copal 1 shutters do not need spacer rings.

The OP's Caltar II-N 180 is mounted in a Copal 1 shutter.

My Compur 1 Electronic seemed to need one. I ended up using a rubber band in a pinch. Maybe that one is a special case in #1 size shutters though.