I expect this question could go in any forum having to do with shooting or reloading but as I saw it mentioned in another thread in this BP forum I'll ask it here.
First off I've been reloading for near 40 years and shooting cast bullets for more than 30 of those. That includes a lot of rounds fired with fillers of various kinds, Cream O' Wheat, cornmeal, dacron, kapok and the foam filler as described by Grahme Wright in his excellet book on loading for double rifles. I make no claims to be an expert but I believe I'll understand what is being said.
What gives with fillers? I tend to believe most who use them are experienced and careful handloaders who pay attention to detail. So, why is it that one or several reloaders can shoot the same load with filler for years and for no known reason one time the same load will ring a chamber? It seems that has happened with all fillers with the possible exception of Grex.
Not to cast aspersions on anyone but I wonder if on some of those occasions a step was left out of the process? I don't believe that to be the case all the time but surely in some small percentage that must be true. I do believe there is something more going on than a lapse of attention. Is there some way to know if a particular load is going to ring a chamber? I doubt it but if there is I'd be pleased to know.
The biggest reason I ask is that for some number of years I have been using the packing foam filler alluded to earlier. To me that seemed the epitome of a filler. It was light, 2 grs., held the powder against the primer, disintegrated upon firing, was cheap and easy to come by and was exceedingly easy to work with. Recently a handloader friend whose opinion I respect told me perhaps I shouldn't be using the foam any longer. He had heard or read of a ringed chamber by someone using foam. I might also ask for a learned opinion of foam fillers.