My mizuno mx23's have a muscle back 8 9 and pw, and cavity backs 7-3i. I strike an 8i pure it flies 178 but the 7 goes 160 on a pure strike. I think it is the cavity back. Has this ever happened to you? I have had the clubs tested and verified my results. What should I do?

some issues you can run into with a mixed set is consistence some clubs feel different in your hands compared to other clubs. i have a mixed set but i keep my irons the same and my wedges all the same brand i have a different brand of driver than i do 3 wood. but if you are playing well with a blended set then go for it. they are not going to ask you if you have a matching set when you post the course record...

Don't mean to question you, but when manufacturers make their sets, be it a uniform set, or a blended set (muscle back on the short irons, cavity on the mid irons and hybrid to replace long irons) they make sure that the set gives progressive yardage difference if hit properly. I.e. hit with similar swing speed, similar position on the club face, similar angle of attack.

If you're 8i gives you 178 and 7 gives you 160, I would take it back to the manufacturer / shop and get them to replace your set.

OR

Paint your 7 with the number 8 and vice versa, so now you have progressive distance. :-)