How to avoid a select query for holding a Sch-S lock

I am looking for an option to avoid Sch-S locks when running a Select query. I have a database which is controlled by an application written by others as well as my own application. One of the tables has millions of rows. I don't have any issue with dirty reads etc. but I don't my select query to lock the other application indexing or modification queries that have to wait due to Sch-S locks from my query. I tried to set isolation level snapshot before calling my query but that didn't make any difference either WITH NOLOCK option that still acquires an Sch-S lock. I am looking for an option to run a select on a table without acquiring Sch-S or any kind of lock, maybe if we can quickly have snapshot/view or temp copy (will it work as it has millions of rows of data?) of the table without acquiring any kind of lock at all.