Actually, a single layer, split pin is known as a "spring pin". They are Q&T high carbon steel. A "roll pin" is made of a softer, ductile alloy that begins life as a narrow strip and is rolled up into a cylinder. Both styles pin are over nominal diameter when in their free state. The spring pin is forced smaller by driving or pressing into the holes in the pieces being joined, but will return to near free state diameter when removed. The softer roll pin also shrinks when inserted, but will not return to free state diameter. Most applications recommend replacement of any roll pins, but allow for reuse of spring pins.
In the OP question, if it is a tapered pin hole in question, it is wise to purchase a reamer specially made for the purpose. They are sized per the pin designed to fit them. Most tapered reamers benefit from drilling the hole in graduated steps to relieve the load on the reamer, not forcing it to cut any more than necessary.