Accurate Arms ranks the shotgun primers, in order of increasing strength, this way:
REM 209P..........Medium Strength
CCI 209..............Medium Strength
WIN 209.............Medium Strength
CHED 209..........Medium Strength
FIO 616..............Magnum
CCI 209M...........Magnum
FED 209A..........Magnum
Weaker primer, same powder / wad / shot combination, lower pressure, right? In a shotgun shell, its not quite that simple. Going over some Hodgdon data, I found it is usually that way but there are quite a few instances where a load with a primer of lesser strength actually produded a higher pressure than the identical load with a hotter primer. Alliants loading data shows the same thing. Those instances arent real common, but theyre there, and some of those loads were already near SAAMI max average pressure.. So, attempting to predict what effect a component substitution will have on pressure could be a mistake, especially when the combination doesnt react in what we would consider a normal way.
Shoot safe.