I've had pretty good luck with a Doe in heat bleat. early rut. They say it also works for late rut, but I've never tried it. The trick is timing and duration of the bleat. 3/4 or 1/2 an hour before legal sunset in the evening. The object is to get the Buck moving before sundown. Don't overdo it, a double bleat with a thirty seconds pause between bleats with long pauses 5-10 minutes between repeats. If the Buck doesn't show up within three retries you can pretty much forget it. If they are within a quarter mile it's likely they will show some interest. If your lucky they will come charging in to have a look. I don't need a caller, I do a pretty good imitation without one.
One oddity is I've had some big ones show up later in the morning as it starts to warm up. I'd give it try near the end of my normal hunting hours 10 AM or even later, kind of a why not last try type thing, that has paid off occasionally.
Works out better if you've heard an actual Doe in heat bleating, you can get the duration and timing right. Don't overdo it, think pleading not manic.
The best Buck I ever got was at 3 PM on a warm afternoon. A Doe had been standing right on top of a bald hill bleating for attention most of the morning and into the afternoon and yes I did let him finish first.
