Hey guys,
I am trying to figure out what could be the culprit of three broken irons in the span of 7 months. Let me give you guys some background:
1. Whole iron set are Titleist 718 AP1s with Tour AD 65i Flex S graphite shafts. These were bought in 2013 after getting custom fitted at a Titleist retailer.
2. These clubs were purchased when I was young. Graphite shafts were installed because of an issue of transferring weight through my swing due to a malformed left leg. The idea was to use graphite to help gain some power and create lag. I swing like Gary Player's step through drill.
3. 9 years later I am much stronger, swing speed is up, and so the graphite shafts feel a bit whippy to me, but I hit them quite pure. The AP1s are pretty forgiving though...
4. I played a decent amount from 2012-2017. Took a break until just about 1 year ago. Since getting back into it last year, 3 irons (7,8,9) have all broken in the exact same place right at the hossel (see pictures).
5. I moved coast to coast in 2019. My clubs were taken on the airplane in a hard shell case. There was a lot of care to make sure the clubs were bouncing all around, but maybe something could have happened during that trip.
6. When each iron broke, I felt them weaken before the head came off. The clubs had a different feel when struck, and the head felt noticeably wobbly. Only one head came flying off, the others just fell off from a light pull. It almost felt like an aging thing was at play here as the head sort of crumbled away from the shaft. It was not entirely clear if there was a crack. The joint at the hossel felt super weak when they were ready to go.
Side tidbits of info:
1. I hit at ranges with mats. Its the only thing I have near me 
2. I do occasionally leave my clubs in my car during the week so they do get exposed to heat. Ferrules have moved around from epoxy expansion but thats jut cosmetics.
Pretty much, all three irons have broken in the exact same way.
Looking closer at the tips of the shafts, the graphite tip itself looks a bit "worn". Similar to what you get when you have old dried up and cracking rubber. Maybe these shafts have just aged over time? Not sure.
If anyone has an idea as to what could be happening (I know you don't know how I swing, but I promise I am not whamming these puppies into the ground). Currently debating reshafting the entire set but at that point it may be worth it to invest in a new set of clubs.