You have an early iteration of the line, almost certainly pre-war. When introduced in the mid thirties it was Comoy's highest grade of pipe. They were all, such as yours, straight grain pipes. Your COM stamping, and the graining of the pipe are consistent of the period where they were Comoy's king-of-the-heap.
The Royal Comoys did not remain the highest grade for very long, as the Blue Riband was introduced shortly thereafter. Your pipe, if it came out of the factory after the early 40's would have the Riband stamping.
The Royal Comoys line was progressively downgraded until it ended up as an essentially entry level Comoy, not a second, but nothing spectacular. All high grade Royal Comoys are stamped in ROYAL COMOYS, most (but not all) of the later, lower grade versions were stamped ROYAL COMOY without the S. All of them have straight, vs. curved COMOY stamps regardless of the era.
This is a great pipe, is it the one on ebay a while back?
PS The shamrock is an unknown stamp to me.