This is really hard to pin down, it changes depending on how you clean your gun and what products you use and what metal preseverative or oil you use, also one of the key factors can be what powder you use.
I personally don't like squib loads or fouling shots so I tried different things till I found a way to avoid them and had to do it all over again when I switched most of my inlines to BH209. Its a personal preference. Lee