Callaway PreOwned 2004 Big Bertha w/ Steel - 4-10,W Iron Set 4-10 Big Bertha Irons with Steel If these irons were any easier to use, they would swing for you The Ultimate in Forgiveness with the Maximum in Distance. A 360 variable undercut channel improves perimeter weighting and delivers a solid feel. For a low center of gravity Designed with added aesthetics.ble Face Thickness technology that optimizes face thickness to concentrate more weight toward the bottom of the club head