I agree..... nothing to worry about.... ie.... Goex FFF.
I just wouldn;t advise using Blackhorn in a plunger. But in a sidelock?...... five grains down the chute and add a little more under the nipple, should be fine. But good ignition would depend on the condition and design of the sidelock - quality of the nipple and cap.... and I would never exceed 95gr loose Blackhorn volume, in a 50-cal sidelock.