I'm just begining to reload and have noticed what seems like excessive powder residue or some type of fouling in my barrel when cleaning. The rifle is a 416 Rigby and I'm using 100 Grains of H4831SC. Is this normal?

what's excessive, how are you measuring the amont of fouling? Burning 100gr of powder is going to leave residue.

Probably normal, and sometimes seems one shot and a clean shows about as much powder fouling
as 10 shots or more.
jl.