This Year's Swing Issue

I game the Mizuno MX-25 irons.  For anyone unfamiliar, they have a significant pocket cavity in the long and mid irons and a much shallower cavity in the short irons.  I'm having trouble with the long and mid irons, but am almost 100% consistent with the short irons.  Obviously I'm very happy with my performance with the 8-PW, but need some help with the 5-7 irons.  I can pick up the 8 and hit a great shot but not the 7.  I always seem to hit the 5-7 thin or just completely chunk it.  I've never had this problem before.  Do I need to use a different swing (maybe shallower?) swing with the 5-7?  Maybe the problem is in my head?  Any feedback would be great.

Sounds like a psychological block as there should be no difference in swing between the 7 and 8.  Unless, you are changing something, like your stance or ball placement.  Are you doing something differently for the 5-7 irons to get these results?  Maybe you are, and don't know it.  Possible?

I do that with my 4 iron. My instructor told me it  was a power move. Somehow I got it in my head that I needed to swing harder. He suggested hitting 6-10 balls with a wedge to slow down then swing the 4 iron, rinse and repeat and build on that feel.

I think it was a combination of my head and using my arms too much.  I grabbed my PW, hit a few balls, then repeated the same stroke with my 5 iron, and much better results.  Didn't get the distance I wanted out of the 5 but the balls were flying properly.

I also hit the entire bucket without a glove to force myself to slow down.  I think that helped a little.

As far as I know, there are only four power moves in golf, the accumulators (there is a nice instruction article in the wiki section that defines them). Quite noticably absent is amount of coil in the backswing and moving way off the ball. I've had the same problem as you and it was due to making a huge swaying backswing coil and then, as a result, starting down with the shoulders. This move will allow you to hit short irons and top/chunk the longer clubs. Resist the shoulder swing to start the transition! The best it can give you is a bullet of a thin shot and the worst is a broken right wrist.