I don't use filler with 4198, or with any other type of powders that prove to
be position sensitive in the case for reliable ignition.

Filler just increases your pressure...

I also don't use mag primers in these reduced loads..

Small Rifle or Large Rifler primes have proven to more than up to the task
in any instance I have used them in...

And yes, I have experimented with Mag Rifle primers, Pistol Primers, Mag Pistol primers...
so I have compared them....and prefer Regular rifle primers....

I don't buy into the full case is best theory...

"Minus the killings, Washington has one of the lowest crime rates in the Country" Marion Barry, Mayor of Wash DC

“Owning guns is not a right. If it were a right, it would be in the Constitution.” ~Alexandria Ocasio Cortez