I've only used 7977 in maybe half a dozen rounds from the .243 Winchester to a couple of .30-06 length belted magnums, but so far it doesn't seem all that primer sensitive. This is true of many extruded powders, which tend to be less primer-sensitive than sphericals. But I also haven't shot it across as wide a variety of temperatures as I prefer before coming to any conclusions.
Have done all shooting so far in "normal" to 90-degree conditions so far, but am waiting for fall to test it in temps around zero, as in my experience powders (and primers) don't act the same when only the ammo is chilled and not the entire rifle.
But I can say that so far 7977 seems to be a very good addition to the powders in the H4831/RL-22 to Magnum/H1000/7828 range.
