Bucks have already done most of their ritual habits, like making scrapes and rubs and are now starting to abandoned those areas and seek does. They are also territorial, so I'd try a regular buck grunt. You may catch a buck ready to fight and your grunt call just may be enough to coax him in. It may also work in the last stages of the pre-rut to try rattling hard. Imitate a good buck fight. This too has proven itself to bring in trophy class animals at the right time!
One simple call that has worked for many, is the Can call.
Just tip it over and tip it back! If a buck is looking for a doe, the Can imitates that better than I can. LOL!
Good luck,
iSnipe