Light primer strikes can be caused by not following thru on the trigger pull, a full pull to the rear is required, or the transfer bar will fall and prevent full impact to the firing pin, just don't release the trigger at the break, exagerate your trigger pull, that should help.
All I shoot is rifle and mag rifle primers, never had a problem, but there's always the possibility of a weak hammer spring, if you feel like replacing it, might as well do a trigger job while you're at it, IF that's the problem, give H&R a call and see if they'll send you one, or you can order them from Brownells or Numrich, they're about $2 each. Wolff also offers heavy duty springs.
Tim