Never heard of but two reasons for ignition problems with black.
1st & foremost "WET" powder.
2nd; fire not getting to powder, most common on a ML'er with a plugged flash channel.
If black Powder is dry & gets a spark, it goes "BOOM", & it'll still do it 100 yrs from now if those two conditions are met.
Could moisture have seeped in around the primer??

Miller/TN
I Didn't Say Everything I Said, Yogi Berra