Tim; Black powder & nitro powders are two entirely different items. It is true that pressure is pressure & cares not how produced. the other side though is that black powder burns about as well unconfined as confined. nitro powders are "Slowed" down by either grain size or retardant coatinngs or both. Powders designed to "Burn slow" most often do not have real good "Low Pressure" burn characteristics. They are especially designed to burn slow under normal conditions with heavy loads applied. You could load a ½oz load in a 10ga with FG black & it would burn & expell the shot out the bbl. Try an equivelent charge of something like Blue Dot & you would most likely have the charge stuck just ahead of the chamber. Alliant lists loads (at least they did, haven't checked their very latest guides) of less than 7k psi "Only" in loads specifically listed as "Target" loads & adds a disclaimer that they may not perform well at low temps. Unfortunately all powder makers aren't as honest.
