Sorry, I've been away for a while. My cases all get deprimed then tumbled in crushed walnut shells. Then I go through each one individually and clean out the primer pocket and the flash hole.
About the only thing I can think of is that I previously attempted to load the 45-70 with RL7 and had this happen several times. (I was talking to an acquaitance from work the other day and he had the same thing happen to him with his 45-70 and RL7. I would have been informative to see if this was the same lot of RL7.) It could be possible that this one loaded cartridge with the older RL7 got somehow mixed in with the H4198 loads. I never mix loads but I guess anything is possible. I've fired hundreds of rounds of H4198 loads out of this rifle without any problems previously.