I have been shooting an 1874 shiloh 45-70 for about 10 years and shot a C Sharps 1885 in 38-55 for couple years before selling it.
I have shot 100% smokeless, RL-7, and it works fine.
Have a 50-70 1874 shiloh on order. Shud be done very soon. I have shells loaded with RL 7.
If you follow published loads it seems to work fine.
