Haven't used pellets for many years. Actually, used them the first couple years Pyrodex came out with them so those with better memories then I will know how many years ago that's been.
At any rate, when I and the guys I shot/hunted with used them(pellets), on occasion, we would experience 'light' ignition problems...'light' as in the rifle would fire but you knew all the powder did not ignite. Some of us did a series of changes to our inlines going from #11 percussion caps to musket caps for hotter ignition. This seemed to help but did not cure the problem.
A call to Pyrodex ensued and this was the explanation:
" The pellet is designed to burn from the inside out via the hole in the center of the pellet. When two pellets are loaded, the holes in the pellets line up in the bbl and if one or both pellets are crushed or for whatever reason these holes don't line up, a squib or light ignition may occur regardless of type of ignition system used. "
We continued to use pellets till my buddy, after hunting hard for a couple days, pulled up on a deer and experienced another 'light ignition' and that was it. Back to the loose stuff.
Maybe things have changed since then. Don't know.
Not knocking the pellets or those that use them...to each their own.
This has been my experience.