This is true especially where the upper part of the bench contains rock that is difficult to break or is of a different type. The difference between a violent blast and one that fails to fragment the upper zone properly may be a matter of only a few feet of stemming. Collar or direct priming (placing the primer at or near the collar of the blast hole with the blasting cap pointing toward the bottom of the hole) of blast holes normally causes more violence than center or toe priming and requires the use of a longer collar distance.