There are two reason to use 2nd Ab- you want to save money by having many primary Ab and one labeled 2nd Ab, or when you want to amplify the signal of your target. The latter is in the case of low abundant proteins, but this is not the case of Actin. So if you have a labeled Ab again Actin you don't need a 2nd Ab.

Yes, I guess that your anti-B actin antibody is already associated with HRP

thank you