stevholly, you need to trim shafts differently for any of the bore through Callaway irons or they will be stiffer than you may want. I originally set the flex standards for irons in my big book (Golf Club Design, Fitting, Alteration and Repair, page 604, 4th edition). This called for normal trimming instructions when an irons shaft tip would be 1” above the ground/sole line where it stopped in the hosel. On a Callaway iron, the shafts tip is around 3/4” lower than the standard, so it needs to be left approximately 3/4” longer when trimming it. You actually should measure the tip location on any iron to adjust the tip trimming properly if you are looking for the standard flex.
The frequency machine is the best way to measure and/or determine a shafts playing flex. Frequency basically takes into consideration the length of the club; the shafts flex properties and the head weight. So, if you simply removed your 5.5’s from your current set and installed them in the Callaway’s, they would play around 1/2 flex stiffer. You would also need to add a butt extension as they would also be 1/2” shorter in length than you original length due to greater shaft penetration.
