I won't try to critique your ammo or gun. I will simply tell you that I shoot S&W Model 627s in competition frequently using moonclips and 38 Short Colt brass from Starline. I load very mild loads using Vihtavouri N310 (3 grs) and Bayou Bullets 160 gr LRNs. Primers are always Federal small pistol. My primers look like yours after firing. I suspect the flatening/dishing of primers is purely a function of the physics of moonclips and frame-based firing pins.

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Bob.
SWCA 1821