Regarding the Colt Officer's ACP that has been returned to me after 35 years, what are the two or three most effective factory cartridges using heavier bullets that the Officer's ACP 3.5-inch barrel can use efficiently?

Speer 230gr short barrel

Federal 230gr HST by double tap

Just search for 45acp short barrel ammo one can find all the information you need.

My experience (having two of them) is that they are rather picky about feeding and tend to break a bit easily.

As far as which round, you need to ensure it feeds reliably. One of the two I have only feeds FMJ ball ammo reliably- and this after several trips to the gunsmith.

The other tends to loose its sights if shot too much, and I’ve had to replace the bushing a couple times.

I shot the second some as a BUG in IDPA, so it does have more rounds than normal in it, but my experience was such that if they were not inherited guns, I’d have sold them.

The commander length guns work much better than the officer’s and at least to me, are about equally concealable.

Not quite an apples to apples answer.

The hydra shocks fed in the more functional gun, but things came apart more frequently (like within 100 rounds) and most of what I shot was 185 LSWC’s at lower velocity, and even then it wasn’t reliable like a government model is. It did not like Speer or hornady ammo for me.

I don’t know what your definition of reliable enough for defensive use is, but it doesn’t make mine.