Pushing 4227 past the accepted handgun magnum pressures of ~35 kpsi there are no "unburned kernals".
Using WLR primers in .445SM loads running around (a calculated) 40-45 kpsi,
the case and barrel may have a trace of ash but it is no more than any other rounds I have ever shot including factory rifle loads.
I have never heard of "filllers" being used in modern smokeless powder.
We have used inert fillers such as Grex to fill up the case when there is a lot of air in there
but it usually gets blown out of the case and gun completely.
Do you have a reference to 4227 having some inert component?
Or have I misread your comment?
4227 does seem to work best with heavy for caliber bullets and a case full of powder.
The magnum primer suggestion is a good one to experiment with although 4227 is supposed to be easier to ignite than say, most ball powders.
I am using rifle primers in the .445 which are doing the job.
The Starline brass got their pockets drilled a little deeper.
I like IMR4227 a lot. It delivers low SD, ES, and high accuracy.
In recent experiments with A1680, I can get maybe 50 more fps but the velocities are all over the place.
ES of 100 fps and over in some loads!
After trying magnum rifle primers 1680 finally gave some lower SD but only at the very top end and nowhere near as low as 4227.
It behaves a lot like a slower version of W296 which is pretty much what it is: a clone of W680.
Some of you may have read my rants about slow ball powders in revolver rounds.
This experience has not changed my opinion what so ever.
I am sticking to 4227 for any serious loads.