5.56 Reloading Question

I reloaded a few 5.56 IMG (Guatemalan) once fired brass.
Used 25 grains of WCC 846 powder and 55 gr boat tail bullets from Weideners.
The powder label showed a max charge of 26 grains. The sierra folks said to use BLC(2) powder data which shows 27 grains as a max load and 25 grains as a starting load.
When I fired a few rounds (10) 2 of the 10 rounds showed no bulges but some cracking / splitting just below the shoulder, only enough to be visible to the eye.
My concern is that on these cases, when I went to clean and deburr the primer flash hole it was too small to get the deburring tool into.
I checked some Remington 223 cases and some LC brass to see the size of the flash hole. both were were larger than the IMG - same size as my flash hole deburring tool .
Don't flame me guys, but I forced the deburring tool to open up the flash hole. At the time it seemed the thing to do....now maybe not. Anyway, do you think that opening up the flash hole could be causing some excessive pressure problems or something?
My estimate is that I need to back off of the powder a little more, but the flash hole thing made me wonder.
I am going to chrono. a couple of rounds next week with a friend of mine to see if the velocity is excessive. I will also try lighter powder charges
Any thoughts or advice would be appreciated.