My grandpa gave me an Excel single shot in 20 gauge. It looks just like your shotgun. He said that he bought it from Higgen's Hardware in 1935 and paid almost 6 dollars for it. I shot my first squirrel with it, Many years after he passed away, I set out to kill a deer with it. I remembered him telling me how he had killed deer with it, but that it shot Foster slugs low and to the left. That, it did. Very reliably. I took my first buck with it. My youngest son took his first deer with it when he was 9.
Shoot yours and see how it performs. If it doesn't group well for you, buy slugs from a different manufacturer. I had to do that with mine until I found a slug which grouped satisfactorily.
I once shot a squirrel out of the top of an 80 foot tree with a slug by accident. Reached in the wrong pocket. Right before that, I shot a running squirrel on the ground with a slug. I thought that a was shooting #6 shot until saw that the runner was nearly cut in half. It was a 30 yard shot.
I then proceeded to pick up my empty shells and noticed that they were slugs. I still struggle to be humble after that day.

I have been slug hunting over 30 years
even when the state went rifle , we hunt opening weekend in a shotgun and pistol only township.
so we have tried a bunch of slugs and such mainly Foster/rifled slugs.
I start with Win super X rifled slugs in any new gun they seem to work the best in everything I have tried them in
I do like the federal sabots , I liked the Winchester dual bond sabots as well they shot good but got near impossible to find
but this isn't a discussion on sabots

you want the rifled slugs they are basically a lead thimble so that they can squeeze down through most any choke

by the way the rifling basically imparts no spin or a negligible amount of spin but it gives room for them to squeeze down as needed without spiking pressures