There are two large flash hole sizes
The really LARGE hole-like just short of the internal lip to stop the primer from passing clear through when priming I have not tried at all.
Like someone mentioned above they were used for plastic/rubber/wax bullets for practice. I would/have not loaded those kind.
Then you have the larger than normal primer hole-about 50% larger. These I tested with Winchester 230gr JHP bullets and Longshot powder at 6.7grs and OAL of 1.20" all had full radius on the primers edge-no flattening at all. I used Winchester, CCI-300 and Remington #2 1/2.