The MP that is common amongst all Mizuno muscle back irons stands for Mizuno Pro. This is the high end line at Mizuno which is designed for players with low handicaps who strike the ball out of the center of the face consistently. Additionally, these model irons are designed to have higher ball flights and better feel to help low handicap players shoot lower scores. , Although it has the appearance of a blade, it is really a hollow head with a copper underlay for feel, Chromoly inside the metal for strength and speed, and tungsten inside to help with forgiveness and launch. The 7-iron has a loft of 30 degrees, which gives it more speed and carry than the 221 and 223 irons, however tests conducted outside seemed to indicate that the ball flew the highest of the three versions. , Historically, Mizuno has made some of the best blades in golf under the MP line. This year's new line in the Mizuno Pro 225 may be the best they've created. These are blade irons but have the thickest profile of their counterparts in the 223 and 221. These irons have been forged with Chromoly, some of the strongest metals used in golf. This has created some of the highest ball speeds of any blade or blade-like iron on the market.