Deep Hole Drilling is used to create holes in relatively large depth to diameter ratio. Normal drilling techniques only work where the depth is just more than five times the diameter.
Gun drilling is a deep hole drilling procedure which is performed with the help of a long and thin cutting instrument to drill holes in the metal with higher diameter to length ratio.
Deep hole boring is the process of enlarging a hole that has already been drilled by deep hole drilling or deep hole gun drilling. The process of boring is performed to achieve the accuracy of the desired diameter.