I`ve measured the thickness of CCI 550 spm & CCI 400 srp (standard small rifle)
They are the same , but my findings are the 400 are a step hotter.
I have devloped loads with some of the dirtier powders & cleaned em up a bit while using em in "mid range" loads . I`m certain if you push the envelope with srp most if not all pistol/shotgun/small rifle powders would build peak pressures very qwikly .
Do I regularly use srp no . Could I get by with just srp yes, but you better believe I`d have a supply of chrono batteries though !!