Just tried Magtech blue box 357 ammo in a 60-15. About one out of five FTF, some after multiple strikes. Primer light dimple. Gun has the standard factory hammer spring. Put those same rounds in my 686 no dash and they fire fine. No problems with Hydra-Shok 357, Hydra-Shok 38 and Remington UMC 38, just the Magtech.
Think I may try an extended length firing pin from Cyl & Slide. Think that will resolve the problem?