How are Koopman and Koopmann connected and seperated

Question

My grandfather dropped the last n after coming to Tomah WI via Ellis in late 1800s

Comments

Spellings back in the 1800s depended very much on which clerk was writing the record. I shouldn't worry too much about whether there is one N or two. Just record each person with the last name at birth and put any variant spellings into the other name field.