loose powder.. I have not had any problem at all with the Remington Kleenbore Primers setting it off. I shoot 120 grains of Triple Se7en 2f in my Knight Disc without any problem. There could be a problem with pellets if there was a lot of moisture. Not that they will not set them off, but if hunting I would want a hotter primer like the Winchester W209 if hunting with pellets. The Remington's and loose powder seem to be made for each other.