870 read my earlier post of what I thought of APP powder.
http://www.graybeardoutdoors.com/phpbb2/viewtopic.php?t=73886As far as the Clean- Bore primers being cleaner, I didnt notice that much difference between these and Winchester either. I heard that Remington designed these to minimize the notorious crud ring" the 777 shooters speak of so much. I have never shot 777 so I dont know.
As for the gritty condition you speak of, ok lets face it, just about all sabots are hard to push down a tight bore besides the power belt type. I know this for sure, I used to shoot black and it was very hard to push the second shot let alone the forth. I also shot a lot of Pyrodex and it was very hard to push the third shot. The APP was by far the easiest foe me. And the bullet youre shooting is a big boy (340 grain) the heavier the bullet the more resistance you will have.
APP says that grit is a natural lube left behind from the burning process to make the next shot easier to load. Hey the way I look at it if you and I are getting these good group who cares about the grit. Grit-R-Done, Hope this helps.