Howdy, Pard,
Actually, I'm surprised that the one carbine has that light a trigger pull. The basic Spencer lockwork is based on the Sharps lock, and they (at least the originals) are quite heavy due to the mainspring pressure on the sear. Unless you have a set trigger, you really have to put up with a fairly heavy (compared to a Winchester lever action) pull. The main thing that stoning the sear contacts can do is insure a smooth pull, but not necessarily very light! Matter of safety.