I need to replace the middle 42t ring on a Shimano triple (RX100 A550-T) I was given a Origin 8 42t (none ramped and pined) and it just does not want to shift from the 26t low to the 42t middle. Must I get a ramped and pinned 42t for it to shift correctly, and will an FSA 42T be compatible with the inner and outer Shimano rings?

It shifts form the 26t to the 42t middle with the original ring without issue, but it is very worn.

I have long used non ramped chainrings, on my triple crank bikes with friction bar end shifters.

The indexing shifter scheme was designed as a system,
and as such you probably do need a pinned and ramped chainring..

Sometimes you can find at bike shops, take offs that people had them remove
a decent, long wearing, steel chainring , because the customers wanted a lighter one..

Non-ramped/pinned is fine. The FSA with the right BCD will work well too. However, FSA rings are soft and tend to wear faster.

Thanks! Just got back from my LBS, and he had a pinned and ramped take off hanging over his workbench, and it shifts flawlessly.

Glad you got it resolved. For the benefit of future researchers, I think the problem is tooth height. Origen 8 rings are for single speeds like bmx and have taller teeth to keep the chain from coming off accidentally. You should be able to shift up from one OK but not up to one. If this is wrong, hope someone corrects this for posterity

tall full height teeth were what chainrings were, before the engineers began work
on making them shift with the rider involvement of driving a car without a clutch.