There are a fair amount of W. Förester offerings out there. I think Heym had the thought of replacing the selector, as found on hammer Dreilings prior to 1891, with a 3rd trigger. So the end user had to decide whether to go with a traditional selector for the 3rd shot or to follow Heym with a 3rd trigger on the new fangled hammerless platforms.

https://www.germanhuntingguns.com/archives/archive-forster-foerster/

Serbus,

Raimey
rse