Over crimping plated bullets is a "problem" that is highly overrated. So is the limitation to 1,200 FPS! After being concerned about these things for many years shooting Berry bullets I decided to just see what would happen. This is what I did: These were .357 Magnum loads.
This was all at the same time for worst case scenario! I loaded the bullets with a full charge, 16+ grains of H110/296 that is supposed to develop ca. 1,600 FPS, well over the Berry 1,200 limit. Second I crimped the loaded rounds to the maximum possible with the Lee CFC die. This was so severe that I could feel and feel when the copper plating was cut through! The die was adjusted so the shell holder bottomed out hard on the die, it couldn't get any more crimp. I then fired these through a 6 1/2" Model 27, and they chronographed just under 1,600 FPS. These were shot from rest at 100 yards.
Out of the 20 rounds so loaded only a few showed any evidence of jacket separation on the target, only 3 or 4, showed that the jacket had formed "petals" that showed on the target. Accuracy was about what would be expected for this distance, under 6".
Copper is extremely ductile. My conclusion from this test, it is extremely unlikely the plating will be damaged by a moderate crimp. Quit worrying about it!