Depends on how you hunt them,
W/ a caller set back from you, it's very possible your shots can be under 20yrds. Now if you hunt solo, things can be a lot trickier, which tells you shots are more likely to be further than the caller set behind you method. Remember, a lot of times bull's will stop and rake a something on their approach. This can be the break you're looking for, try to approach him as quickly as possible while he's occupied w/ raking. They will usually have their eyes closed and the noise from battling the brush can give you an advantage.